To evaluate the growth regulatory effect of chlormequat chloride (CCC) under drought stress conditions on three barley cultivars, a field study was conducted under Badjgah agro climatic conditions (altitude 1810 m, longitude 52° 46´, and latitude 29° 50´) during 2003-2004 growing season. A randomized complete block based split- split plot of four replications was employed with two moisture levels (well watered and drought stress during the post anthesis period) as main plots, chlormequat chloride treatment placed in sub plots (control and 1370 g a.i. ha-1 at lemma primordium stage) and 3 barley cultivars (Reyhaneh, Karoon and Valfajr) as sub-sub plots. The results indicated that drought stress decreased the grain yield, biological yield and harvest index of barley cultivars. The effect of drought stress on yield components, except for the number of grains per spike, was significant. CCC enhanced grain yield under well watered conditions, however, under drought stress conditions it decreased the grain yield significantly. The number of spikes m-2 was increased in CCC-treated plants. Dry weight and leaf area decreased under drought stress conditions. Green leaf area and dry weight of CCC-treated plants were greater during post anthesis period. Although a deep understanding of the effect of CCC on grain yield under drought stress conditions needs more research and for longer periods, it became evident that the timely use of CCC in irrigated barley farms could result in to an increased grain yield.