Although many studies have established the connections of the inferior olivary complex, there have been relatively few studies on the morphology of this nuclear complex. On the base of the similar topographic relations and connections with the cerebellum, the inferior olivary complex is regarded as homologous in all vertebrates. We present comprehensive light microscopical qualitative and quantitative analysis of the inferior olivary complex of different representatives of submammalian and mammalian vertebrates, including human. A detailed comparison was made at the structural level. Cytoarchitecture and cellular morphology of the inferior olivary complex have been studied in several submammalian (carp, frog, lizard, tortoise, pigeon) and mammalian species (rat, cat, and for the first time ground squirrel Citellus citellus L), including human.