Abstract This paper examines weight patterns in tri-syllabic words within a Moraic-theoretic account. A word weight pattern is weight of syllables and is defined based on distinction between heavy and light syllables (Carr, 2008:172); Here, the notion of mora (symbolized μ) as a basic timing unit provides a distinction between 'light' and 'heavy' syllables. Hayes (1989:356) mentions that heavy syllables have more moras compared to light ones. Also, there are some weight alternations in the syllabic patterns of Persian tri-syllabic words; that is, in an alternative weight pattern, syllables are distributed so that weight is alternately high and low. In order to study and compare weight patterns of simple, derivative and compound words, about 32 thousand tri-syllabic words were collected from Dehkhoda (2003) and Moshiri (2009) dictionaries. Then, they were sorted in an Excel worksheet with all phonological information, including weight of syllables (light, heavy, super-heavy, and ultra-heavy). Also, alternative and non-alternative weight patterns were specified. Results indicate that there happen 49 weight patterns in tri-syllabic words and syllables of one mora (mono-moraic), two moras (bi-moraic), three moras (tri-moraic), and even four moras (tetra-moraic) are probable. However, the sequence of mono-moraic and bi-moraic syllables is the most frequent and tri-moraic and tetra-moraic syllables, especially adjacent ones, are less frequent. This indicates that tri-syllabic words tend towards short syllables. Moreover, the non-alternative quasi-monotonic weight patterns are the most frequent ones. Likewise, simple words ideally tend to sequences of mono-moraic and bi-moraic syllables and tetra-moraic ones are loanwords; the derivatives are heavier than the simple and lighter than the compounds. Keywords: Syllable Weight, Mora, Derivative, Simple, Compound, Tri-Syllabic. Introduction Weight pattern of a word is the weight of its syllables and is defined based on distinction between heavy and light syllables (Carr, 2008:172). Mora is a basic timing unit that link prosodic and segmental information, represented by the root node. Mora is equal to or shorter than a syllable and the weight of the syllable does not depend on the number of segments in the syllable but the number of moras in it. Heavy and super heavy syllables are of more moras compared to light syllable with one mora; for example, a short syllable such as ‘ba’ consists of one mora (mono-moraic), while a long syllable such as ‘baa’ consists of two (bi-moraic). Such metrics are also referred to as syllable weight (Hayes,1989: 356). In Moraic Theory, only rhyme constituents contribute to the weight of the syllable and are tied to moras (µ), while onsets are tied directly to the syllable node (σ) with no role in weight (Hyman, 1985: 145-6). According to Kambuziya (2006:135) “in moraic theory, short vowels bear one mora and long vowels bear two moras are not considered phonologically light at all.” In this connection, Ghorbanpour (2019) and Salimi (2018) studied the weight pattern of bi-syllabic and tetra-syllabic words. Granted with this and many other studies, we shall study and compare the weight patterns in different kinds of tri-syllabic words including the simple, derivative and compound in Persian within a Moraic-theoretic account. Thus, firstly, we shall overview the main tenets of the theory, syllable weight, and the alternation of weight in syllabic patterns. Then, we shall specify the distribution of tri-syllabic words’ weight pattern and the alternative and non-alternative patterns. The main problem of the study is to examine the distribution of weight patterns in simple and non-simple words derived from a large corpus of 32 thousand tri-syllabic words. The present study is also aimed at investigating whether there are any meaningful relations between the number of syllables, word formation, and the moraic weight patterns. Materials and Methods The research data includes a set of 32 thousand tri-syllabic words in Persian collected from Dehkhoda (2003) and Moshiri (2009) dictionaries. The words were sorted in an Excel worksheet with all their etymological and phonological information, including the weight of syllables (light, heavy, super-heavy, and ultra-heavy) and the number of moras. Then, alternative and non-alternative weight patterns were determined. Discussion and Conclusion The present study eximaned the distribution of weight patterns of tri-syllabic words, including simple, derivative and compound words. Findings suggest that there happen 49 weight patterns in tri-syllabic words and syllables of one mora (mono-moraic), two moras (bi-moraic), and three moras (tri-moraic). Interestingly, the results show that even four moras (tetra-moraic) are probable in Persian. However, a sequence of mono-moraic and bi-moraic syllables - the pattern 1,2,2 - is the most frequent. This is while syllables of tri-moraic and tetra-moraic, especially the adjacent ones, are less frequent. This is an indicative of tri-syllabic words’ tendency toward short syllables. Also, simple words often tend to sequences of mono-moraic and bi-moraic syllables and those with tetra-moraic ones are generally loanwords. Moreover, the derivatives are heavier than the simple and lighter than the compounds. Thus, the number of heavy syllables probably increases through the transition from simple words to complex ones. For a more accurate categorization, the non-alternative patterns were divided into monotonic, quasi-monotonic, ascending, descending, and disordered. Results indicate that non-alternative quasi-monotonic patterns are the most frequent weight patterns in all kinds of tri-syllabic words.