The leopard slug (Limax maximus Linnaeus, 1758) is a slug of the Family Limacidae, native to Europe and the Mediterranean Sea. It is mainly found on ships and crops and has been introduced worldwide, and was first confirmed in South Korea in August 2023 in Suwon, Gyeonggi-do. Although the route of introduction is challenging to estimate, it is believed to be highly adapted to the domestic ecosystem, as a large number of individuals were identified at the time of discovery. As a species that causes global damage through competition with native species and transmission of zoonotic diseases, there is an urgent need for research on this species. Therefore, in the present study, we investigated the potential for establishment and spread of the leopard slug in South Korea and identified its introduction route through genetic diversity studies. As a result of the distribution survey, we identified the population up to 1㎞ from Bambat Green Frog Park, where the first population was confirmed, and a total of 1,060 individuals were identified in an area of about 2.3㎢. Among them, mitochondrial DNA COⅠ was analysed from 27 individuals, and the genetic diversity was very low at 0.00271, and the mitochondrial haplotype was consistent with the UK and Switzerland. Body length measurements of individuals identified during field surveys showed that March was statistically significantly smaller than August, with a mean of 27.9㎜ (N=160) in March and 73.3㎜ (N=549) in August (p<0.01). Although we were unable to confirm domestic breeding of the spotted slug, the seasonal variation in size of the individuals identified suggests that domestic breeding is suspected and the potential for domestic establishment is very high. Based on the low genetic diversity of the species and the fact that no additional habitat has been identified outside the 2.3㎢ surrounding the area of occurrence, it is considered an early stage invasive species. However, due to the location of the Bambat Green Frog Park, which is a stronghold of the spotted slug, and its ecological characteristics of feeding and resting in food waste and domestic and agricultural refuse, there is a high probability of unintentional spread and future nationwide distribution of this species, and immediate management of this species is required.