Endocrine disrupting chemicals are a serious concern all over the world. In this study, the endocrine disrupting effects of commonly used insecticides thiamethoxam and lambda cyhalothrin were investigated by using Oreochromis niloticus as a model organism. The fish exposed to 1/20, 1/10 of 96-h LC50 value of thiamethoxam and lambda cyhalothrin (477.29 mg/L, 2.901 mu g/L), individually and in mixtures, for 7 and 15 days. Fish were then left to depurate in pesticide-free water for 7 days. Results showed that acetyhcholin-esterase, catalase and estradiol/testosterone levels decreased, while the amount of etoxyresorufin-O-deetylase (EROD), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione (GSH) and protein carbonil (PCO) increased in comparison to the control. After the recovery period, EROD, GST, malondialdehyde, estradiol/testosterone levels were found to be lower than the control. In the pesticide mixture group, the activity of antioxidant enzymes was highest and the level of hormones was lowered. The group of the mixture pesticide showed the highest lipid peroxidation and protein carbonylation than only thiamethoxam or lambda cyhalotbrin exposure. In conclusion, the mixture of the insecticides showed a more toxic effect on the gonad of tilapia compared to individual pesticide exposures. In addition, the depuration period of 7 days was not adequate to eliminate the toxic effects of these insecticides.