This study was carried out to investigate the flora of Mt. Suan (Gyeonggi-do). The vascular plant were collected 13 times (from March to October 2011), and 402 taxa in total were identified, including 102 families, 274 genera, 354 species, 6 subspecies, 40 varieties and 2 forms. Among them, 8 taxa of Korean endemic plants and the Korea Forest Service-designated rare plants were identified as 5 taxa. Based on the list of plants which have been approved for overseas delivery, 10 taxa were recorded in the investigated area. The Ministry of Environment-designated specially plants were identified as 17 taxa. The naturalized plants were identified as 41 taxa and the percent of naturalized index (NI) was 10.2% of total 402 taxa vascular plants.