Effective and safe delivery of small interfering RNA (siRNA) by nanomaterials to cancer cells is one of the main challenges in cancer treatment. In this study, we constructed the selenium nanoparticles conjugated with RGDfC (one tumor-targeted polypeptide) to prepare a biocompatible gene vector (RGDfC-SeNPs) and then loaded with siDCBLD2 to synthesize the RGDfC-Se@siDCBLD2 for colorectal cancer (CRC) therapy. As expected, RGDfC-SeNPs could enhance the cellular uptake of siDCBLD2 in human HCT-116 colon cancer cells by targeting polypeptide RGDfC on the surface of colon cancer cells. RGDfC-Se@siDCBLD2 could be effectively internalized by HCT-116 cells mainly through a clathrin-related endocytosis pathway. In addition, RGDfC-Se@siDCBLD2 exhibited high siRNA release efficiency in an acidic tumor environment. Moreover, RGDfC-Se@siDCBLD2 could inhibit the proliferation and induce apoptosis in HCT-116 cells by special silencing gene DCBLD2 expression. RGDfC-Se@siDCBLD2 could be specifically accumulated to the tumor sites and exhibited significantly anti-CRC efficacy on HCT-116 tumor-bearing mice without obvious side effects. Taken together, these results suggest that selenium nanoparticles can be used as an effective gene vector with good biocompatibility, and RGDfC-Se@siDCBLD2 provides a promising strategy for combining tumor-target and siRNA delivery in treating CRC.