β-catenin, a key factor in the Wnt/β-catenin signaling pathway, is involved in gonadal development and differentiation in fish. In this study, the full-length cDNA sequence of β-catenin2 was for the first time cloned from the FFRC strain common carp (Cyprinus carpio) by RACE-PCR, and expression patterns of β-catenin2 in various tissues and in the development of gonad were investigated. The results showed that the full-length cDNA sequence of β-catenin2 was 3 411 bp, encoding 780 amino acids with a predictive molecular weight of 85.52 ku; Quantitative real-time PCR demonstrated that:β-catenin2 mRNA expressions were high in gonads and the expression increased as the gonads developed in the early development stage. Testosterone (T) treatment increased the relative β-catenin2 mRNA expression level at 10 μg/g 24 h treatment in the ovary. The β-catenin2 mRNA expression decreased at 10 μg/g 24 h, 48 h and 50 μg/g 24 h, 48h testosterone treatments in the testis. 17β-estradiol (E2) treatment had no significant effect on the expression level of β-catenin2 mRNA in testis and ovary (P > 0.05). These data suggested that β-catenin2 is an essential protein in gonad early development of C. carpio.