A review of the literature on the study of rhetorical questions (RQs) shows that most of the previous studies are aimed to describe the pragmatic function, while the cognitive factor has been considered by relatively few researchers. The major goal of this study is to discuss the syntactic category of RQs under the Prototype Theory of Categorization. The author first set up a theoretical frame for analyzing RQs, suggesting that all grammatical structures are prototypical categories, which fall into a category of syntax, a category of semantics and a category of pragmatics and a category of syntax is a category of different semantic meanings and pragmatic functions expressed by the same syntactic form. An analysis of RQs shows that RQs and genuine questions are in the same syntactic category—QUESTION because they share syntactic similarities. Keywords: rhetorical questions; the Prototype Theory of Categorization; syntactic category of RQs