Diazinon (DI) is an organophosphate. Thymoquinone (TQ) is produced from Nigella sativa: This study was a biochemical investigation of the protective properties of TQ as a supportive treatment in brain damage caused by diazinon. Rats were divided into four groups of eight, as follows: Group 1, control; group 2, DI; group 3, DI + TQ; and group 4, TQ. Groups 2 and 3 received DI. Groups 3 and 4 received TQ. In group 2, NO levels were higher and SOD levels were lower compared to the control group. In groups 3 and 4, NO levels were lower and SOD levels were higher than in either the control or group 2. In group 4, DNA damage was lower than in group 2, but the difference between groups 2 and 3 was not significant. The results suggest that TQ, because of its antioxidant properties, can be used to treat oxidative stress caused by DI intoxication.