Objective To investigate the expression of insulin-like growth factor-Ⅱ（IGF-Ⅱ） mRNA-binding protein-3（IMP3） in tissue of benign nevi and malignant melanoma, and to evaluate the role of IMP3 in the development and diagnosis of malignant melanoma. Methods Immunohistochemistry was performed to measure the expression of IMP3 in tissue samples from 28 cases of malignant melanoma, 8 Spitz nevi, 6 dysplastic nevi and 25 benign nevi. Results Immunohistochemically, IMP3 was observed in 23 of 28 melanoma samples, 4 of 8 Spitz nevus samples and 2 of 6 dysplastic nevus samples, but not in benign nevus samples. The expression level of IMP3 was significantly higher in tissue of melanoma than in that of Spitz nevi and dysplastic nevi （both P < 0.05）, also higher in tissue of aggressive melanoma than that of melanoma in situ（P < 0.01）. Conclusions IMP3 seems to be a biomarker for the progression of benign nevi to malignant melanoma, and may be utilized to distinguish melanoma from benign nevi.