The present investigation aimed to assess the allelopathic effects of aqueous leaf extracts of Datura stramonium L. (family: Solanaceae) on seed germination, hydroxyl radical (• OH), activities of some metabolic enzymes and antioxidants levels of both Trigonella foenum-graecum L. (fenugreek, family: Fabaceae)and Lepidium sativum L. (cress, family: Brassicaceae).The results revealed that Daturaaqueous leaf extract inhibited seed germination and retarded the activities ofthe following enzymes: glucose-6-phosphate dehydrogenase (G6PD, EC.1.1.1.49), 6-phosphogluconate dehydrogenase (6PGD, EC.1.1.1.44) and adenosine triphosphatase (ATPase, EC.3.6.1.3). However, Datura aqueous leaf extract enhanced NADH-oxidase (EC.1.6.3.1) activity in a concentration-dependent manner. Also, Datura leaf extract enhanced production of OH radical and antioxidants including proline, α-tocopherol and reduced glutathione (GSH) but decreased oxidized glutathione (GSSG) content.