The present work through light on the role of allelopathic potential of Calotropis procera on some growth and physiological parameters of three cultivated crops. The selected species, namely; cucumber, tomato, and wheat were grown in a pot experiment under six different concentrations of aqueous leaf extract ranged from 0 % to 50 % (w/v) with 10 % intervals for one month after seedling stage. The data obtained revealed a significant reduction in shoot and root length, which was higher in the root than shoot and the inhibition rate among studied species were in the order of tomato>cucumber>wheat. The plant fresh and dry weight showed a significant inhibition in both tomato and wheat and a nonsignificant and especially at low concentration. The species response was in the order of tomato>cucumber>wheat and tomato>wheat>cucumber for fresh and dry weight respectively. A variety of responses in the pigment content in which tomato>cucumber>wheat and wheat>cucumber >tomato for chlorophyll and carotenoids respectively. Allelopathic stress stimulates the accumulation of study metabolites soluble proteins, amino acids and proline by the same manner in all target species wheat>cucumber >tomato except for soluble carbohydrates; cucumber>wheat> tomato. These data may confirm the response of wheat to the allelopathic stress of Calitropis procera was lower than tomato and cucumber were in between, and the target species tend to accumulate these metabolites as an adaptive strategy to alleviate the allelochemical stress of Calitropis procera.