Morphological characteristics of most of the species included in the Heterakidae family are similar. The study of the ultrastructure of helminths makes it possible to determine additional taxonomic features in the identification of species. In the present study, the ultrastructural characteristics of the organs belonging to the reproductive system of adult female nematode Heterakis dispar (Schrank, 1790), belonging to the Heterakidae family, with using of light and electron microscopic methods were studied. It was found that the wall of ovary, oviduct and uterus consists of two (basal lamina and epithelial), vagina has three (basal lamina, muscular and epithelial), and the wall of the ovijector consists of four layers (basal lamina, muscular and epithelial, thick cuticle in the lumen). The ultrastructural characteristics of helminth germ cells and their development (oogenesis) in different stages (oogonia, oocytes) were studied in detail. The layers of the formed eggshell of H. dispar nematode (uterine, vitelline, chitinous and lipid layers) were determined. In the study, a comparative analysis of the ultrastructure of reproductive organs of female H. dispar with nematodes H. gallinarum and H. spumosa, which belong to the Heterakidae family was given. It is appropriate to use the obtained results in specifying the systematic positions of nematodes. In the future, ultrastructural data can be used as a norm during the development of methods of combating nematodosis.