Formalin is widely used in industry and in medicine (as tissue fixative and disinfectant).It contains reactive molecules which have been known for its cytotoxic effects. To evaluate the effect of formalin exposure on the testicular tissue and sperm parameter from neonatal period through physical and sexual maturity, 28 male Wister rats were assigned into two equal test and control groups. The test group was exposed to 1.5 ppm of the vapour of 10% formaldehyde in a special chamber for 2 hr per day at 20-26 ˚C and the air pressure of 760-763 atm. After 55 days, the tubular differentiation (TDI) and repopulation (RI) indexes in testicular tissue, sperm quality parameters, serum total antioxidant capacity and testosterone level were determined. The formaldehyde-exposed animals showed severe seminiferous tubules atrophy, edematous connective tissue, arrested spermatogenesis with negative TDI and RI and vascular thrombosis compared to control group. Histomorphological studies showed a high sperm mortality and abnormality associated with a remarkable decrease in sperm count. Formaldehyde-exposed animals revealed with decreased serum level of testosterone (p < 0.05) and down-regulated antioxidant status versus control group. In conclusion, the current data provide inclusive histological and biochemical information about the chronic exposure to formaldehyde with emphasizing on reproductive disorders including histological adverse effects on the testicular tissue, spermatogenesis, sperm viability, count and the abnormalities which can potentially cause infertility after sexual maturation.