In this study, morphological changes in the ovaries of guinea pigs during postnatal development were investigated. The study population was consisted of 56 female guinea pigs which were divided into seven groups according to the age; 1 day, 2,4,6,12,18 weeks and older than 18 weeks. Each group was composed of 8 guinea pigs.

A significant correlation was found between the age and the body weight (r=0.99), the age and left ovary weight (r=0.95) and between the age and right ovary weight (r=0.98). It was observed that the ovary germinative epithelium was consisted of simple cuboidal or low columnar cell types. Polyovular follicles and polinuclear oocytes were not observed. Zona pellucida was found to be P.A.S. positive.

At the 4^th week, for the first time the follicles with antrum appeared. Theca interna and externa were obvious in secondary follicles and in follicles with antrum.

Medulla was consisted of loose connective tissue and it contained several different sized blood and lymph vessels, nerve fibers surrounded by elastic fibers.