Ring-tailed lemurs (Lemur catta) are popular exhibit animals in zoos. During the breeding season, males may fight strongly and this may end up with serious wounds and/or escapes. The hormonal contraceptive deslorelin, a GnRH-agonist, has been used in different species to suppress reproduction. This contraception strategy can reduce the production of sexual hormones and therefore, it could be used to control aggressive behavior. Here, we analyzed the effect of a 4.7 mg deslorelin implant on the testicular function in five male ring-tailed lemurs. The aim of the study was to assess if this contraception strategy could be used to reduce testosterone levels and thus aggressive interactions within individuals. Neither testosterone concentrations detected in feces nor spermatogenesis evaluated by testes histology was suppressed by the deslorelin treatment. The present study has shown that a GnRH implant containing 4.7 mg deslorelin has no contraceptive effects in ring-tailed lemurs. The use of different dosages of deslorelin implants as well as the effect of other hormonal contraceptives should be evaluated in this species.