The establishment of invasive alien species management is widely recognized as a pivotal issue in the preservation of biodiversity. Ranunculus sardous Crantz, a species native to Europe, has been widely introduced in many other areas of the world, including the coasts of the United States, Australia, China, India, and Japan. In Korea, the first population of this plant was found growing adjacent to a wetland in Hanon, Seogwipo-si, Jeju Province, on 22 May 2018. Field observations confirmed the presences of at least two populations of this species in Jeju Province, Korea. This species is similar to Ranunculus sceleratus L., but can be readily distinguished by its presence of the trichomes in the whole plant, longer petioles of radical leaves, ovate-shaped leaf segments, globose to subglobose-shaped fruits and flat achenes with narrowly winged and papillae. The Invasive Alien Plant Risk Assessment (IAPRA), a system for recognizing and categorizing alien plants in Korea forests, was used to assess the invasiveness status of the species. Based on this system, R. sardous received a low score of 6, suggesting its potential invasion to natural forests. Although the current distribution of R. sardous is restricted to Jeju Province and thus far has had limited impact on local environments, local and regulatory authorities should pay close attention to this plant and take measures to prevent its further expansion.