The aim of the study was to evaluate the effects of protein deficiency on plasma testosterone levels, epididymal sperm characteristics and testicular histology in the developing male rat. Twenty four Wistar albino rats were used in the study and were fed with a diet variously containing 3%, 10% and 20% protein. Plasma testosterone levels were significantly lower in rats fed 3% protein when compared to rats fed 10% and 20% protein (P<0.05). Testicular weight in protein deficient rats (rats fed 3% and 10% protein) was significantly lower than that of a control group (20% protein) (P<0.05). No sperm was present in the epididymal duct lumen, but germ cells were observed in some duct lumens in rats fed 3% protein. Epididymal weight decreased significantly in rats fed 3% protein compared to rats fed 10% and 20% protein (P<0.05). The results of this study clearly show that protein deficiency in developing male rats adversely affects gonadal endocrine function, testicular histology and spermatogenesis.