The present study focuses on understanding the role of different antioxidants in plant defense against oxidative stress caused by fenoxaprop-p-ethyl herbicide. Besides ameliorative effect of exogenously applied salicylic acid (SA) and selenium (Se) on fenoxaprop-p-ethyl-induced toxicity was examined in Avena sativa L. It was determined that the MDA (malondialdehyde) content in the groups to which only herbicide was applied was higher than that of the groups to which SA and Se applied together with the herbicide. In plants exposed to fenoxaprop-p-ethyl, the activities of peroxidase (POD), ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione S-transferase (GST), glutathione reductase (GR) and content of glutathione (GSH) increased in the treatment groups compared to the control groups. The antioxidant activity increased in the control and treatment groups that were pre-treated with SA and Se compared to the groups that were not pre-treated with SA and Se. While catalase activity (CAT) decreased in SA pre-treated plants, it increased in Se pre-treated plants. These results indicate that the fenoxaprop-p-ethyl induces various plant defense responses in target plants and that treatment with exogenous SA and Se can increase stress resistance by altering these responses.