During two successive seasons of 1997 and 1998, water requirements of cucumber (Cucumis sativus L.) grown in clay soil under unheated plastic house were determined based on Class A pan method with or without polyethylene mulch. Water application of three levels were (75%, 100% and 125% of Class "A" pan) and three polyethylene mulch colors were used (Black, Silver, transparent and bare soil). The vegetative growth, i.e., plant height, leaf number, and leaf area together with yield were determined. Soil temperature was also recorded. The results showed that high level of water gave the highest vegetative growth, K content and total yield in comparison with other treatments. On the other hand high water treatment (125% of pan) resulted in a significant decrease in Na content of cucumber leaves. Concerning polyethylene mulch, results showed that silver plastic mulch gave the highest vegetative growth in comparison with clear and black polyethylene mulch but highest yield was recorded with black polyethylene mulch.