Abstract: Z1820 is a rice resource of clustered spikelets but Jinxiang1A, Jin2A, and Jin4A are normal. Three F1 combinations and 3 F2 generations of normal/clustered were obtained in crosses of Jinxiang1A/Z1820, Jin2A /Z1820 and Jin4A /Z1820. And three backcrosses were produced by using Jinxiang1A, Jin2A, and Jin4A as recurrent female parents. The main results showed: all F1 combinations performance a middle degree of clustering character and F2, BF1 generations represent segregation in clustering degree; the character of clustered spikelets in Z1820 is controlled by a part-dominance gene but a genetic factor in Jin4A can affect the expression of clustering. Clustered ratio was proposed firstly to characterizing clustering degree.