Abstract: Background and Objective: Several medicinal plants are reported as having allelochemicals potentials and favorable results have been obtained in this regard. The present investigation aimed to evaluate the effect of different concentrations of leaf aqueous extract of two medicinal plants, Artrmisia monosperma and Thymus vulgaris on growth criteria, physio-biochemical attributes and antioxidant enzyme activities of pea (Pisum sativum L.) seedlings. Materials and Methods: Germination of pea was performed in Petri dishes under different concentrations (0, 2, 4, 6, 8 and 10%) of leaf aqueous extracts of the two medicinal plants collected from natural habitats in Saudi Arabia. At the end of experiment (10 days), the growth and physio-biochemical characteristics of pea seedlings were measured. The data were statistically analyzed by one-way ANOVA analysis of variance using SPSS program. Results: Leaf aqueous extracts of A. monosperma and T. vulgaris reduced germination capability, shoot and root length, total free amino acids and proline content. Contrariwise, there was an increase in carbohydrates, proteins, K+, Ca2+ and the activity of antioxidant enzymes. Lipid peroxidation and H2O2 contents were significantly enhanced with increasing concentrations of both extracts. The highest inhibitory or stimulatory effects of leaf aqueous extract were observed at concentrations 8 and 10%. T. vulgaris was more effective than A. monosperma. Conclusion: This investigation indicated that the two medicinal plants had allelopathic compounds with strong potential, which may play important role in weed control and used as an alternative of chemical compounds. The aqueous extract of T. vulgaris has allelopathic potential more than A. monosperma and could be evaluated as an allelopathic species.