Many recent studies have reported on the effects of learners' mental operation on the propositions of the rule on rule learning. This article argued that operational thinking was extremely important in rule learning, and showed that the reason why this factor had not received the attention in past studies was the researchers' narrow viewpoints on rule learning. In addition, the article proposed a classification of the operations into three categories: variable operation, relational operation, and abstraction operation. Finally, recent studies on the operational thinking and rule learning were reviewed and some directions for future study were suggested.