Abstract:Three hundred and sixty hybrid F1s from 4 indica (IR36 and Nanjing 11) and japonica (Balila andAkihikara) rice as female parents crossed with the rest male parents were used to study the spikelet fertility inrelation to Cheng's index difference (ID) and to isozyme genetic distance (GD). The results showed that ID and GD significantly negatively correlated with F1 spikelet fertility (r=-0.540, p<0.01; r=-0.316, p<0.01), but thedeterminative coefficient was low, which was 0.2916, 0.0999, respectively.