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Skeletal muscles consist of heterogeneous fibers with various contractile and metabolic properties that affect meat quality. The size of muscle fibers contributes to muscle mass and myopathy. Thus, improved understanding of the expression patterns underlying fiber size might open possibilities to change them using genetic methods. The aim of this study was to reveal transcriptomic landscapes of one oxidative (Psoas major) and three glycolytic (Longissimus lumborum, Triceps brachii, and Semimembranosus) muscles. Principal component analysis (PCA) showed significant differences in gene expression among the four muscles. Specifically, 2777 differentially expressed genes (DEGs) were detected between six pairwise comparisons of the four muscles. Weighted gene co-expression network analysis (WGCNA) identified six modules, which were significantly associated with muscle fiber diameter. We also identified 23 candidate genes, and enrichment analysis showed that biosynthesis of amino acids (bta01230), sarcomere (GO:0030017), and regulation of actin cytoskeleton (bta04810) overlapped in DEGs and WGCNA. Nineteen of these genes (e.g., EEF1A2 , FARSB , and PINK1) have been reported to promote or inhibit muscle growth and development. Our findings contribute to the understanding of fiber size differences among oxidative and glycolytic muscles, which may provide a basis for breeding to improve meat yield. • Comparisons of functional enrichment results were conducted. • Transcriptome differences among glycolytic and oxidative skeletal muscles are important for determining muscle fiber size. • Muscle fiber diameter was determined, and candidate genes related to it were identified using WGCNA. • The more detailed results in the supplementary materials strengthen our understanding of oxidative and glycolytic muscles. [ABSTRACT FROM AUTHOR]