Abstract: Zhu`s genetic model of endosperm characters and statistical approaches of conditional genetic variances were used to analyze the genetic regulations of grain-filling rate for inferior and superior grains of rice including three NPT sterile lines and two restoring lines with NC-Ⅱdesign. The results showed that for the superior grains, VG was the main variance component, highest in the early stage. Endosperm effect was the major form in the early stage, and cytoplasmic and maternal effects were more important in the middle and late stages. The active time for each conditional variance component was VA（t∣t-1）in the early and middle stages, VC（t∣t-1） in the middle and late stages , VAm（t∣t-1） in the whole filling stage and VDm（t∣t-1） mainly in the early stage. For the inferior grains, only in the middle stage VG was more than VGE, and the main variance component was also from endosperm variances. This result indicated that the inferior grains were more likely to be influenced by environments. The expressing characters of gene effects were? VD（t∣t-1） and VAm（t∣t-1））expressing significantly in the early stage and VAm（t∣t-1） being more important; VAm（t∣t-1） being less than VAmE（t∣t-1）. In the middle stage , VA（t∣t-1）became the most important variance and VAm（t∣t-1）was the second. In the late stage VCE（t∣t-1）became the main variance component. The results between conditional variance analysis and variances analysis of inferior grains were conflicting.

Key words: Japonica, Filling rate, Genetic, Inferior and superior grains, Conditional genetic variance