Because parental lines of rice hybrids usually differ in their growth duration, obtaining well-synchronized flowering is a major problem in hybrid rice seed production. The present method of staggered sowing of parental lines based on their growth duration difference, though simple, is not always effective, especially in areas where temperature changes are frequent. Reports from China indicate that because the leaf number of a rice cultivar is fairly stable, leaf number difference can be used to decide the seeding dates of parental lines in hybrid rice seed production. Before using this method, however, the leaf number of the prospective parental lines to be used in hybrid rice seed production should be ascertained. We conducted an experiment to determine the leaf number of two cytoplasmic male sterile (CMS) lines and five promising restorers during the 1994 wet season (WS), 1995 WS, and 1995 dry season (DS) at the DRR research farm. We also compared the extent of variation for leaf number and days to flowering over the seasons.