To survey the effect of soil irrigation intervals on grain yield, yield components and harvest index of bread wheat cultivars, an experiment was conducted based on randomized complete blocks as a split plot design with 4 replicates during 2006-2007 at the experimental farm of Agricultural and Natural Resources Research Center of Yazd. The main plots consisted of four irrigation treatments (8, 10, 12 and 14 days) and the sub-plots consisted of one line and three bread wheat cultivars (Backcross Roshan, Sistan, WS-82-9 and Pishtaz). The results indicated that the irrigation treatments had significant effects on grain yield, yield components and harvest index and there were significant differences between cultivars in terms of grain yield and yield components. Moreover, the interaction effect of irrigation interval x cultivar on grain yield and harvest index was significant (P<0.01). The maximum yield components and harvest index were obtained in 8 and 10 days intervals. 8 days interval showed the highest mean grain yield, while the lowest mean yield components, grain yield and harvest index were observed in 14 days interval. Comparison of the cultivars showed that Sistan and WS-82-9 had the maximum number of grains per spike and thousand kernel weight, respectively. Pishtaz and Backcross Roshan had the maximum number of spikes per square meter. Also, Sistan and Backcross Roshan had the highest grain yield while the maximum harvest index belonged to Sistan, Backcross Roshan and WS-82-9. Based on the study results, 8 days interval was recognized as a favourable irrigation period for achieving the greatest economical yield in the region, while WS-82-9 showed the greatest drought tolerance and Sistan was the most productive cultivar under well-watered conditions.