We examined the effects of floral organ size on female reproductive success in self-incompatible Erythronium japonicum. We measured tepal size and anther-stigma separation and investigated the relationship between these measurements and fruiting and seeding success. We found that tepal length was positively correlated with fruiting success and the number of seeds per fruit. This suggests that pollinator attraction is affected by tepal length in E. japonicum and that the number of pollinator visits affects female reproductive success. Anther.-stigma separation was the most variable floral trait measured and was not correlated with either fruiting or seeding success in this species, suggesting that the proportion of outcross pollen deposited on stigmas by pollinators does not increase with anther-stigma separation. This is inconsistent with a previous report on Etyyhtonium. grandiflorum. Pollinator size might explain this interspecific difference in the effect of anther-stigma separation on female reproductive success.