This paper proposes a method for investigating the syntactic structure of emergent languages using categorial grammar induction.Although the structural property of emergent languages is an important topic, little has been done on syntax and its relation to semantics.Inspired by previous work on CCG induction for natural languages, we propose to induce categorial grammars from the sentence-meaning pairs of emergent languages.Since an emergent language born in a signaling game is represented as pairs of a message and meaning, it is straightforward to extract sentence-meaning pairs to feed to categorial grammar induction.We also propose two compositionality measures that are based on induced grammars.Our experimental results reveal that our measures can recognize compositionality.While correlating with existing measure TopSim, our measures can gain more insights on the compositional structure of emergent languages from induced grammars.