A study of alien ant species in Khlong Lan National Park, Kamphaeng Phet Province between November 2021 and July 2022 was carried out using pitfall traps in three different kinds of ecosystems: 1) natural forest areas, 2) guesthouse areas, and 3) nature trails. A total of nine alien ant species in seven genera (Anoplolepis gracilipes (Smith, 1857); Tapinoma melanocephalum (Fabricius, 1793); Technomyrmex albipes (Smith, 1861); Technomyrmex difficilis (Forel, 1892); Monomorium floricola (Jerdon, 1851); Monomorium pharaonis (Linnaeus, 1758); Paratrechina longicornis (Latreille, 1802); Tetramorium kheperra (Bolton, 1976), and Trichomyrmex destructor (Jerdon, 1851)) were collected in the national park, and were estimated about 60 percent of all alien ant species occurring in Thailand. Among them, three species, A. gracilipes, T. melanocephalum, and M. pharaonis can be found in all habitats and seasons. The most abundant species was A. gracilipes. This species adapted forging in the natural forests and seems to be an invasive alien species. Seven alien species were collected around the guesthouses, five species in natural forests and along the nature trails. Alien ant species of the national park had the highest diversity and abundance in the dry season and the lowest in the rainy season