Datura stramonium contains allelochemicals which have allelopathic properties that have the potential to inhibit or stimulate vegetative plant growth. Aqueous leaf extract of D. stramonium at 25%, 50% and 100% concentrations were applied to determine their effects on plant height, number of leaves per plant, leaf length, root length and internode length of two maize varieties (Sammaz-39 and Oba super-06) under field conditions. Distilled water (0%) served as control.The treated maize seeds were planted in the experimental field and the plots were laid as randomizedcomplete block design (RCBD) replicated three times.Results on the effects of D. stramonium leaf extract were determined for each treatment concentration. Results showed that D. stramonium leaf extract significantly increased plant height of Sammaz-39 at a concentration of 50% at 10WAP and also of Oba super-06 variety at a concentration of 50% at 8 and 10WAP. Number of leaves per plant was significantly decreased at 10WAP in Sammaz-39 at 100% concentration while Oba super-06 variety showed a significant decrease in number of leaves per plant at 50% concentration at 8WAP. The highest leaf length was observed at 25% concentration of D. stramonium leaf extract in Sammaz-39 at 8WAP and at 25% concentration for Oba super-06 at 2, 4, 6 and 8WAP. But at 10WAP, highest leaf length was observed in the control (0%). Root length was significantly increased in treated seeds of the two varieties; highest root length was observed at 50% concentration in both Sammaz-39 and Oba super-06. Internode length on the contrary, was significantly decreased at high concentration of 100% in Sammaz-39 while no significant difference was observed in the internode length of Oba super-06 variety. This study reveals that high concentration (100%) of D. stramonium leaf extract has inhibitory effects on number of leaves per plant, leaf length and internode length while lower concentrations (25% and 50%) has stimulatory effects on vegetati