Background: Malignant melanoma (MM) is a highly aggressive tumor. Its treatment has been revolutionized by the development of immune-checkpoint inhibitors which targeted at B7 protein or their putative receptors. HHLA2 was a newly identified member of B7 family, but its expression and function in MM was unknown. Herein, we aimed to study its clinical implications and potential regulatory role in MM. Methods: In this study,we examined HHLA2 expression in tissue-arrays containing nevus, malignant melanoma and metastatic malignant melanoma by immunohistochemistry staining. The intervention of HHLA2 in A375 cell line was performed and its effect on the cellular function was also analyzed. Then we identifed the diferentially expressed genes upon HHLA2 knockdown in A375 cell lines by using KEGG and GO analysis. Results: We found that HHLA2 was overexpressed in mucosal melanoma tissues and metastatic melanoma tissues but absent in nevus and cutaneous melanoma tissues. In vitro analysis, knockdown of HHLA2 in human MM cell line inhibited its proliferation, migration and invasion ability. According to the microarray data, MMP3 and NF-kappa B signaling pathway were involved in HHLA2 mediated progression in A375 cells. We confirmed the down-regulated expression of MMPs and core genes of NF-κB signaling pathway upon the HHLA2 knock-down. In addition, we checked the expression of epithelial-mesenchymal transition (EMT) related markers, and found that HHLA2 knock-down induced a MET process in A375 cells. Conclusion: Our findings indicated a novel role for HHLA2 in regulation of the metastatic capacity, which might be a potential therapeutic target for MM.