Abstract: In order to investigate the effect of insulin-like growth factor-Ⅰ (IGF-Ⅰ) on the growth traits of Zacco platypus, IGF -Ⅰ gene sequence was cloned and analyzed. The gene was 13707 bp in length and contained five exons and four introns. The five exons of IGF -Ⅰ were 222, 160, 182, 36, and 829 bp long, and the four introns were 1194, 7771, 254, and 1879 bp long, respectively. The open reading frame was estimated to be 486 bp, encoding 161 amino acids. The results of real-time qPCR (RT-qPCR) showed that the IGF -Ⅰ mRNA in liver tissue was the highest, followed by gonad, spleen, heart and brain, and the lowest expression in kidney. From July to August, IGF -Ⅰ in the sexually mature Zacco platypus gonads increased significantly during the breeding period and fell to the lowest value after the breeding period. The expression level of IGF -Ⅰ in other tissues did not fluctuate greatly during the growth and development process and before and after reproduction. The average expression level of IGF -Ⅰ gene in most tissues of male individuals were higher than that of females. Fluorescence in situ hybridization (FISH) mapping showed that IGF -Ⅰ gene was broadly cytoplasmic-positive and a few were nuclear-positive, showing a full cytoplasmic distribution in liver tissues. It also positively expressed in spermatocytes, follicular membranes and follicular fluid. The above results indicated that the IGF -Ⅰ gene expression pattern of Zacco platypus was gender-specific. It is speculated that the high expression of IGF -Ⅰ in the testis during reproduction is one of the reasons why males are larger than females. The results of this study provide reference materials for the study of sexual dimorphism and artificial breeding of Zacco platypus.