This study was aimed to investigate the protective effects of astaxanthin (AST) against formaldehyde (FA) induced tissue injury on the rat testes. 10 weeks old and weighing 280 (±20) g 32 male Wistar Albino rats were used. The rats were randomly divided into 4 groups. In the Control group, 1 ml of physiological saline solution was injected intraperitoneally, and 1 ml of drinking water given orally. 10 mg/kg 10% FA was applied intraperitoneally to Group II (FA group), Group III (FA+AST16), and Group IV (FA+AST32), and respectively 1 ml drinking water, 16 mg/kg AST and 32 mg/kg AST were given orally to rats in these groups. Testes were stained immunohistochemically PCNA (proliferating cell nuclear antigen), and the TUNEL technique for apoptosis and examined histopathologically for alterations. Total testosterone levels were evaluated by competitive ELISA. Apoptosis and PCNA index calculations and histopathological changes in testicular tissue indicate that FA is the cause of alterations on the testicular tissue. In addition, it has been demonstrated that the AST administration positively affects the prevention of toxic and oxidative damage due to FA in testicular tissue. This study, which was experimented on rats with ELISA testosterone levels and, immunohistochemical alterations in testis tissue, suggested that FA exposure caused the testicular tissue injury.  It has been shown that FA administration causes apoptosis and decreases the PCNA index in spermatogenic cells in seminiferous tubules and Leydig cells responsible for testosterone production.