The rapid growth of global human activities has increased the introductions of nonnative species to an unprecedented level. Among globally documented nonnative species, reptiles and amphibians make up a significant portion. Although the introduction of many nonnative species has been linked to the wildlife trade and stowaways, the origin of introduced individuals often remains unclear. Here, we determined the geographic origin of the second known specimen of Red-banded Snake (Lycodon rufozonatus) found in Jeju Island, Republic of Korea, using phylogenetic analyses. In addition, we assessed the establishment potential of the species through ecological niche modeling. Phylogenetic analyses of two mitochondrial genes strongly supported the origin of the specimen from the East or South Central regions of the People's Republic of China, especially Anhui and Zhejiang provinces, suggesting an introduction through anthropogenic activities rather than a natural colonization from mainland Korea. In addition, the ecological niche models had adequate predictive abilities and estimated suitable habitats across the island, suggesting habitat conditions sufficient for establishment and colonization. The potential sources of introduction are legal and illegal trading, as well as accidental transportation as stowaways. The locations of the two L. rufozonatus recorded are extremely close, suggesting that the species has potentially established itself in Jeju. The introduction and establishment of L. rufozonatus on the island is likely to have negative impacts on the island's native fauna through predation. Therefore, further surveys around the area where the specimens were found and around major ports on the island are required to verify the presence of additional individuals and prevent population establishment.