Two field experiments were conducted at the Experimental farm, Sakha Agricultural Research Station, Kafr El-Sheikh Governorate, during the two successive summer seasons of 2017 and 2018. The work aimed to study the impact of deficit irrigation during various growth stages with magnetized water and their interactions on parameters of vegetative growth and leaves chemical constituents of cowpea cv. Kafr El-Sheikh-1. The experimental layout was split-split plot system in a complete randomized block design with three replicates. The experiment in each season included 16 treatments, representing the combinations of two magnetized of irrigation water (Non-magnetized water (control), Magnetized water), two growth stages (vegetative & reproductive) and four irrigation regime %, i.e. 100, 75, 50 and 25 % of full crop evapotranspiration (ETc), during the two growth stages. Results indicated that cowpea plants, which were irrigated with magnetized water, gave the highest values of vegetative growth parameters and leaf chemical constituents compared with plants irrigated with normal water in both seasons. As for deficit irrigation at different growth stages, all vegetative growth characters and leaf chemical constituents of leaves were decreased with water deficit at vegetive growth stage (v). The plants which irrigation at 100% ETc (2093.14 m³/fed.), followed by 75% ETc (1569.86 m³/fed.) or 50% (1046.57m³/fed.) gave the highest values of vegetative growth parameters and leaf chemical constituent compared with the 25% ETc treatment, which recorded the lowest ones in both seasons. According to the mentioned results, it has been noted the cowpea plant is very sensitive to the water stress at the vegetative growth phase. The best vegetative growth parameters and chemical constituents of leaves were when irrigated the plants by magnetized water at 100% ETc during the vegetative growth stage (v).