This study analyzes the acquisition of relative clauses in Japanese to determine the semantic and functional characteristics of children's relative clauses in spontaneous speech. Longitudinal data from five Japanese children are analyzed and compared with English data (Diessel & Tomasello, 2000). The results show that the relative clauses produced by Japanese children predominantly have stative/attributive predicates. Additionally, early relative clauses in Japanese are often used to identify a referent that is not present in the context of interaction. These findings contrast with Diessel & Tomasello's (2000) English data, and possible explanations include the input that children are exposed to, which reflects typological characteristics of noun modification in Japanese.