The link between language and false belief (FB) understanding has been the focus of considerable debate regarding which language component (semantics, general language, or complementation) is necessary for FB development. We examined the relative roles of complementation and receptive vocabulary in FB development in Korean-speaking and English-speaking children. FB understanding, memory for complements involving the verbs think, say and want, and receptive vocabulary were measured at three time points in 59 Korean-speaking children and 72 English-speaking children. A multi-level growth model indicated that the development of receptive vocabulary and separately the development of think understanding uniquely predicted the development of FB understanding. Neither say nor want was associated with FB understanding. The same pattern was found for Korean- and English-speaking children. The results provide evidence for the role of general language in FB understanding and against the unique role of sentential complementation.