Greenhouse experiments were conducted to discover the effects of the tissue extracts and competition of wheat (Triticum aestivum L.) on the growth attributes of wild oats (Avena fatua L.). Water-soluble toxins from living tissues of wheat significantly decreased the growth attributes of wild oats. In comparison with the control, the irrigation of wild oat plants with shoot extracts resulted in a significant decrease in their total biomass, pigment, carbohydrate and protein contents, but the inhibitory effects of the root extract were nonsignificant. Along with allelopathy, competition has a marked effect on the growth reduction of wild oat plants