Abstract: Protein content of grain for six different varieties was compared at the same phase of grain filling, and the dynamic change of protein content was analyzed at four phases. Meanwhile, the relationship of protein content of grain with grain filling rate was analyzed. The results indicated that there was a fast-increasing period in the course of protein accumulation of each variety, which was usually at the period or last phase, and that XR243 was chosen as the best parent variety with better nutrition quality because of its higher protein content. Correlation analyses showed that there was no significant correlation between soluble sugar content and protein content of grain. That indicated that Carbon metabolism and Nitrogen metabolism were two independent courses from heading to ripening of rice.