Leaf margin serration is a morphological characteristic in plants. TheCUC2(CUP-SHAPED COTYLEDON 2) gene plays an important role in the outgrowth of leaf teeth and enhances leaf serration via suppression of growth in the sinus. In this study, we isolated theBcCUC2gene from Pak-choi (Brassica rapassp.chinensis), which contains a 1104 bp coding sequence, encoding 367 amino acid residues. Multiple sequence alignment exhibited that theBcCUC2gene has a typical conserved NAC domain, and phylogenetic relationship analysis showed that theBcCUC2protein has high identity withCruciferaeplants (Brassica oleracea,Arabidopsis thaliana, andCardamine hirsuta). The tissue-specific expression analysis displayed that theBcCUC2gene has relatively high transcript abundance in floral organs. Meanwhile, the expression profile ofBcCUC2was relatively higher in the ‘082’ lines with serrate leaf margins than the ‘001’ lines with smooth leaf margins in young leaves, roots, and hypocotyls. In addition, the transcript level ofBcCUC2was up-regulated by IAA and GA3 treatment, especially at 1–3 h. The subcellular localization assay demonstrated that BcCUC2 was a nuclear-target protein. Furthermore, leaf serration occurred, and the number of the inflorescence stem was increased in the transgenicArabidopsis thalianaplants’ overexpressedBcCUC2gene. These data illustrated thatBcCUC2is involved in the development of leaf margin serration, lateral branches, and floral organs, contributing to further uncovering and perfecting the regulation mechanism of leaf serration in Pak-choi.