Abstract: This research studied the physiological effects of vanillin on corn and the activity of oxidative enzymes under vanillin imposed oxidative stress. Vanillin is a secondary metabolite which is produced in many plant species. It leaks out of living roots and shoots of donor plants and decaying material of dead plants into the neighboring environment. The 0.0, 0.5, 1, 2, 4 and 8 mM concentrations of vanillin were used as treatments. Seed germination was not affected seriously after 72 h of incubation at 25°C. Surprisingly, the longitudinal root and shoot growth was significantly reduced. This finding shows its phytotoxic effects against neighboring plants in natural and cultivated ecosystems. Besides its inhibitory effects, by an unknown mechanism of action, vanillin imposed an oxidative stress on corn plants. This was demonstrated by elevated malondialdehyde levels which were positively correlated with increased vanillin concentrations. This finding suggests an oxidative role for vanillin in corn which brings about the elevated activities of antioxidative enzymes. A possible mechanism of vanillin action is proposed.