Abstract: We investigated chlorophyll, carotenoid, and soluble sugar contents as well as the mechanical details of antioxidative defence responses in wheat (Triticum aestivum L. cv. Xindong No. 17) seedlings experimentally treated with varying levels of omethoate. The objectives of the present study are to better understand physiological and biochemical responses to omethoate in wheat. For this, wheat seedlings were grown hydroponically for two weeks and subsequently exposed to 0 (control), 0.1, 1.0, 5.0 and 10.0 g/L of omethoate, respectively. Plant samples were collected at 1, 3, 5 and 7 days after treatment, respectively, for analysis of the physiological parameters selected. Results showed that chlorophyll content as well as carotenoid content was decreased with increasing concentration of omethoate, especially as the experiment was progressed. In contrast, soluble sugar content was raised with increasing concentration of omethoate, especially as the experiment continued. The activities of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were increased in the treatments with low concentrations but sharply decreased in the treatments with high concentrations. Moreover, the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) were increased at 0.1 g/L of omethoate on day 1 and then decreased as the concentration of omethoate was raised and the experiment was progressed. In conclusion, wheat could tolerate omethoate stress and could grow normally at low concentrations of omethoate. The possible mechanisms involved might be attributed to higher activities of SOD, POD and CAT, higher soluble sugar content and lower photosynthetic activity, resulting in lower oxidative damage. However, the activities of SOD, POD and CAT were inhibited by the treatments with high concentrations of omethoate. Besides, the activities of APX and GR were promoted in the treatment with extremely low concentrations of omethoate to protect plants form oxidative damage. However, wheat growth was significantly inhibited by the treatments with high concentrations of omethoate.