In order to study the effect of harvesting time on yield of rapeseed cultivars, this research work was carried out at paddy fields of Rice Research Institute of Iran in Rasht andAmol during 2005-2006 and 2006-2007 cropping seasons. The experiment was conducted in a split plot based on randomized complete block design with three replications. Four rapeseed cultivars including Hyola 308, Hyola 401, Hyola 420 and RGS003 were arranged in main plots and four harvesting times in subplots. The criterion for harvesting was the moisture content of the seeds in the siliques of 1/3 base of main stem and moisture content of equal or greater than 40%, 35%, 25% and 15% were used as an indication for harvesting the cultivars. The results showed that Hyola 401 and second harvesting time had maximum grain yield (with average of 2427 and 2367 Kg ha^-1 ), oil yield (1066 and 1027 Kg ha^-1), biological yield (7666 and 7624 Kg ha^-1), harvest index (29.99 and 30.67%), number of seeds in the siliques (25.17 and 25.25) and number of silques in plant (152.7 and 144.9). Hyola 401 in second harvesting time had maximum grain and oil yields and Hyola 308 in fourth harvesting time showed minimum grain and oil yields. Based on the obtained results, Hyola 401 and second harvesting time are superior compared to the other treatments due to fast field discharge for rice planting and having maximum grain and oil yields.