In this study, we have investigated the effects of different doses of thymol (T) and carvacrol (C) on sperm quality oxidative stress and antioxidant system. For this purpose, 49 rats were divided into seven groups (7 rats in each group): 1st Group (control); 2nd Group T-10 (thymol 10 mg/kg), 3rd Group T-20 (thymol 20 mg/kg), 4th Group C-10 (carvacrol 10 mg/kg), 5th Group C-20 (carvacrol 20 mg/kg), 6th Group T + C-10 (thymol 10 mg/kg + carvacrol 10 mg/kg) and 7th Group T + C-20 (thymol 20 mg/kg + carvacrol 20 mg/kg). The duration of the experiment was 10 weeks for all animals. During the study, sperm quality parameters (motility, concentration, abnormal spermatozoa and live–dead sperm ratio), biochemical parameters [malondialdehyde (MDA), reduced glutathione(GSH), glutathione peroxidase (GSH-Px), catalase (CAT), AST, ALT, GGT, urea and creatinine] were analysed, and histopathological examination was performed. The study results showed that monotherapies of thymol and carvacrol significantly decreased MDA levels in testicles, liver and kidney tissues compared to the control group (p < .001). GSH levels increased only with the thymol administration and GSH-Px and catalase activity increased only with the carvacrol administration compared to the control group (p < .05). The combined administration of these two agents did not cause any significant change in any parameter. Regarding the sperm quality parameters, only the spermatozoa concentration and motility increased significantly in the thymol and carvacrol groups compared to the control group (p < .01). However, these parameters decreased in the 7th Group (T + C-20) compared to the control group (p < .001). Considering the dead sperm ratio decreased significantly in the 2nd (T-10), 3rd (T-20), 4th (C-10), 5th (C-20) and 6th Group (T + C-10) compared to the control group (p < .001). In respect of spermatozoon anomaly, there was a significant decrease in thymol and carvacrol monotherapy groups. The histopathological analysis of the testicle, liver and kidney tissues of the animals showed no difference between the groups. In conclusion, we have determined that thymol and carvacrol administration decreased the oxidative damage and increased the antioxidant levels and improved the sperm quality parameters. However, the combined use of these two active ingredients had a limited therapeutic effect on the mentioned parameters.