Leaves grow by distinct phases controlled by gene regulatory networks including many transcription factors. () promotes leaf growth especially during the cell expansion phase. In this study, we identify TCP13, a member of the TCP transcription factor family, as an upstream inhibitor of . Yeast one-hybrid screening using a 1.2-kb upstream region of resulted in the isolation of TCP13 as well as other transcription factors. Transgenic plants constitutively expressing displays a significant reduction in leaf cell size especially during the cell expansion period, while repression of and its paralogs ( and ) result in enlarged leaf cells, indicating that TCP13 and its paralogs inhibit leaf development, mainly at the cell expansion phase. Its expression pattern during leaf expansion phase is opposite to expression. Consistently, the expression of and its downstream genes decreases when was overexpressed, and increases when the expression of and its paralogs is repressed. In chromatin immunoprecipitation assays using plants, a fragment of the upstream region that contains the consensus sequence for TCP binding is strongly enriched. Taken together, these findings indicate that TCP13 and its paralogs inhibit leaf growth by repressing expression.