Abstract: Insulin-like growth factors (Igf) are evolutionarily conserved gene family that regulate a variety of cellular biological processes, including growth, proliferation, survival, migration, and differentiation. To understand the role of igf3 gene in sex determination and differentiation in Culter alburnus, the full-length cDNA sequence of igf3 was cloned by rapid amplification of cDNA ends (RACE) technology; real-time quantitative PCR (qRT-PCR) was employed to analyze the expression level of igf3 in different tissues; DNA sequencing of sodium bisulfite was used to explore the CpG methylation pattern of igf3 promoter in adult testes and ovaries. The length of igf3 cDNA was 901 bp with a 92 bp 5′UTR, a 203 bp 3′UTR and a 606 bp ORF encoding of 201 amino acid residues. Sequence analysis showed that similar to other IGF family members igf1 and igf2, igf3 also had conserved characteristic domains, which were mainly divided into precursor signal peptides, B, C, A, D, and E regions. The expression level of igf3 gene was significantly different in various tissues (P<0.05). The expression was the highest in the ovary, followed by the testis, while the expression abundance was extremely low in the brain, heart, spleen, liver, muscle and kidney. Analysis of CpG islands methylation pattern revealed that igf3 promoter CpGs were not methylated in the ovary, but is hypermethylated in the testis. These findings indicated that igf3 was involved in gonadal formation or functional maintenance in C. alburnus, and the DNA methylation modification in the promoter region of igf3 genome was closely related to sexual dimorphism expression between gonadal tissues.