The experiment carried out in 2007 and 2008 in the Dryland Agriculture Research sub –Institute Sararood, Kermanshah, Iran in order to study the effects of drought stress on yield, proline content, soluble carbohydrates content, relative water content and chlorophyll content of bread wheat cultivars under field conditions. The experiments were base on split plot in a randomized complete block design with three replications. The main plots included drought stress treatments at 4 levels: I1- drought stress at the start of stem elongation stage (31 Zadoks); I2 - drought stress at the start of boot stage (43 Zadoks); I3- drought stress at the start of grain filling stage (70 Zadoks) and I4- full irrigation.The Subplots included cultivars treatments at 3 levels: Chamran (C1), Marvdasht(C2), and Shahriar (C3). A significant difference (p<0.01) was observed between the drought stress treatments. The results showed that with an increase in  the Intensity of drought stress on wheat cultivars, there was a decrease in relative water conten , total chlorophyll content and increased proline content, but was not observed on trend relating to soluble carbohydrates content. The Chamran cultivar (C1) on drought stress treatment (I1) had the lowest decrease in relative water content and total chlorophyll content than with control treatment (I4). Also this cultivar had the highest drought tolerance and yield stability.

Keywords: Bread wheat, Drought stress, Relative water content, Proline, Soluble carbohydrates, Chlorophyll