Abstract: The effects of base applied N and P on starch accumulation, grain starch synthesis enzyme (GBSS) activities and their relations during the grain filling were studied using 4 different series hybrid rice (Byou 827, Hongyou 2209, Cyou2009 and Gangyou725). The results indicated that the variety and N application rate are the two primary factors influencing amylose content. The other factors also significantly affected amylose content. A significant positive correlation was observed between GBSS activities and amylose content. The optimal formula for highest amylase content varied with varieties. The N and K application rates were N180K135, 180K135, N180K180; and N90K180 for Byou 827, Hongyou 2209, Cyou2009 and Gangyou725, respectively.