Abstract: Rice phyC mutants were isolated using a mutant panel isolation method. When the mutants were grown under long-day photoperiodic conditions, it was found that they flowered (exposed their panicles (heads)) about one week earlier than the control rice. The results indicate that suppression of PHYC gene expression can promote plant flowering under long-day conditions. Utilization of the PHYC gene for promoting plant flowering will contribute substantially to breed improvement, for example, by facilitating the creation of useful agricultural crops and decorative plants that have a new characteristic adaptable for other cultivation areas and times. The rice phyC mutants described herein, which promote flowering under long-day conditions, will be highly prized as a new early-harvest rice cultivar.