Purpose. Comparison of dimensional characteristics of various non-wood fibers (flax, hemp, bamboo, cotton), which can be used as an additional component in the production of non-woven composite materials from synthetic fibrous waste. Method. The structure of the fibers was studied by optical polarization microscopy. The dimensional characteristics of the fibers were determined by the method of analyzing digital images, followed by statistical processing and graphical analysis of the obtained data. Results. A quantitative comparative analysis of the transverse dimensions and distribution for this indicator for non-wood fibers of various natural origin: flax, hemp, bamboo, cotton. It has been established that the average transverse dimensions of the initial fibers of flax and hemp are higher than for bamboo and cotton fibers with greater variability of this index and a pronounced asymmetry of the distribution towards valuesgreater than the average. Scientific novation. Based on a detailed statistical analysis of microscopic images, differences in the transverse dimensions of non-wood fibers of different natural origin are established. Practical value. The results obtained can be used to produce nonwoven composite materials with predictable properties. [ABSTRACT FROM AUTHOR]