This study was carried out to determine the different irrigation regime effects on oxygen isotope discrimination of stem water (Delta O-18(s)) and its relationship with grain yield (GY), aboveground biomass (BM), and stomatal conductivity (g(s)) of winter wheat. For this purpose a field experiment was conducted between 2009 and 2011 in a semiarid region of Turkey under rainfed (RF), deficit (DI), moderate (MI), and full irrigation (FI) conditions. The highest GY and BM (4.5 t ha(-1) and 14.5 t ha(-1)) were measured from the FI treatment. However, the difference between the yield of DI and FI treatments was insignificant. It might be recommended that the DI treatment be used for wheat irrigation to increase water-use efficiency for semiarid climate conditions. Average Delta O-18(s) values were obtained as 35.36 parts per thousand, 34.56 parts per thousand, 34.35 parts per thousand, and 33.18 parts per thousand for RF, DI, MI, and FI treatments, respectively. Applied irrigation water and GY were found to be strongly negatively related to Delta O-18(s), so it may be a useful predictor of yield in irrigation programs. Effects of water regime on yield probably reflected the correlation with the isotopic composition of transpiration. A negative relationship was obtained between average Delta O-18(s) and g(s) at a significant level for which the correlation coefficient was 0.68. However, the relationship was positive between GY and g(s).