In order to determine the phenological differences of some for improved rice cultivars in Iran for applying in crop simulation models, an experiment was conducted in the research farm of the Rice Research Institute of Iran (Rasht) in 2020 was performed as a randomized complete block with three replications. The experimental treatment consisted of six rice cultivars (Rash, Anam, Gohar, SA1, SA6 and M7). The results showed that the highest development rate was observed in development rate in juvenile phase and grain filling phase in Anam cultivar. The minimum and maximum time required to start emergence with 3 and 6 days were in Anam and Gohar cultivars, respectively. The maximum time required to achieve maximum flowering and physiological maturity was obtained with 71 and 103 days in Gohar cultivar. The highest flowering period with 19 and 20 days was obtained in late maturing Rash and Gohar cultivars, respectively. The highest growth degree days (GDD) in beginning of grain filling to maturity stage was observed with 401 GDD for M7 cultivar. The highest growth-day for pre-flowering with 1208 GDD belonged to Gohar cultivar. The highest harvest index was obtained with 50.91% in Gohar cultivar. The results also showed that the single grain weight under ideal growing conditions with 0.030 g was observed in Gohar and M7 cultivars. The results showed that the highest plant height belonged to cultivar M7 with 150 cm. The results showed that the highest total nitrogen uptake was observed in the plant at maturity of Anam cultivar.