Whether J. S. Mill is a rule-utili-tarian or not? This question entails vigorous debates since J. 0. Urmson interpreted Mill as a rule-utilitarian. But there was no distinction between rule and act-utilitarianism in the times of Mill, and the nature of moral rule in his text is ambiguous, so this question is hard to be resolved. According to the definitions of various types of rule-utilitarianism, and Mill's Utilitarianism and other related writings, I reexamine the possibility of Urmson's interpretation and its limits.