In utero development of organs is easily influenced by many environmental factors. The aim of this study was to elucidate the effect of microwave radiation (MR) at a frequency of 2.45 GHz and a specific absorption rate of 1.73 W/kg on intrauterine development of testis. Pregnant albino rats were exposed to whole-body MR for 2 hours per day throughout the pregnancy. Male offspring (n=12, age 35 days) were not exposed to MR after birth. The study revealed that MR applied in utero induced apparent structural changes in the testes, such as irregular shape of seminiferous tubules, significant decrease in the diameter of seminiferous tubules (p<0.05) and in the height of the germinal epithelium (p<0.01), disorganisation of germ cells, desquamations of immature germ cells, formation of giant multinucleated cells, and significant (p<0.01) expansion of the interstitium. At the level of transmission electron microscopy, there were observed basement membrane irregularities in seminiferous tubules, vacuolation of the cytoplasm and adversely affected organelles in Sertoli cells, germ cells, Leydig cells, peritubular and endothelial cells. The tight junctions between adjacent Sertoli cells were often incomplete, and necrotizing germ cells were more numerous in experimental animals compared to controls. Enhanced necrotizations of germ cells proved by a Fluoro Jade C method, and declined germ cells proliferation confirmed by proliferating cell nuclear antigen analysis, were detected in MR exposed animals. Our results revealed that the prenatal exposure to MR had an adverse effect on the postnatal testicular development in rats.