To determine the effect of planting date on yield components as well as yield in three rice cvs., a factorial design based on a randomized complete block design with four replications was employed in Veisian region during the 1997-98 growing season. The three rice cultivars–Domsyah, Tarom and Anbarboo were sown at four different dates from 2 May to 1 June within an interval of 10 days. Results of ANOVA showed that planting date had a significant effect on paddy yield, biological harvest index as well as all yield components with the exception of single grain weight. Delayed planting dates resulted in a decrease in panicles/plant followed by a decrease in seed/panicle and single seed weight. Paddy yield decreased with delay in planting date (2 May). Results showed that harvest index has a high effect on paddy yield. With delay in planting date and in contrast to decrease in biomass, harvest index increased. Differences between studied cultivars in view point of yield components, biomass and harvest index were significant at 1% probability level. Anbarboo cv. has the highest panicle/plant (7.791) as well as seeds/panicle (120.0) and Domsyah cv. was panicles/plant (R=0.633*), grains/panicle (r=0.840**), biomass (r=0.473*), and harvest index (r=0.873**). Variation of paddy yield was independent of single grain weight (r=-0.222).
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