The aim of this study was to determine the effect of deficit irrigation on yield for pepper grown under unheated greenhouse condition. The research was carried out at the Agricultural Research Station of Yenisehir High School of Uludag University in Bursa, Turkey, in 2007. In the study, water was applied to pepper as 100, 75, 50, 25 and 0% (as control) of evaporation from a Class A pan (K1(cp) 1.00, K2(cp) 0.75, K3(cp) 0.50, K4(cp) 0.25, K5(cp) 0.00-control) corresponding to 2-day irrigation frequency. Irrigation water applied to crops ranged from 65 to 724 mm, and water consumption ranged from 115 to 740 mm. The effect of irrigation water level on the yield, fruit heigth, diameter and weight and dry matter ratio were significant. The highest yields were 24 and 19 t ha(-1) for the K1(cp) and K2(cp) treatments, respectively. Crop yield response factor (k(y)) was 1.07. The highest values for water use efficiency (WUE) and irrigation water use efficiency (IWUE) were 3.13 and 3.39 kg mm(-1) for the K2(cp) treatment. Under the conditions that water resources are scarce, it can be recommended that K2(cp) treatment is most suitable as a water application level for pepper irrigation by drip irrigation under unheated greenhouse condition.