Genotypic and phenotypic variances, and covariances were estimated among five characteristics of 12 early maturing genotypes of grain sorghum in a double cropping of spring and fall season in Japan. The differences among genotypes and genotype × season interaction were significant for almost all characteristics. A large proportion of the phenotypic variance, which was attributable to genotypic variance, was obtained for plant height, 100 grain weight and grain yield. The highest genotype × environment interaction was detected for days to heading. Harvest index had a negative correlation with plant height and positive correlation with grain yield, phenotypically and genotypically. This correlation analysis may provide useful information in the selection of sorghum genotypes with high yield and short plant height for a double cropping system in Japan.