The study was carried out to assess the occurrence, invasion and usage of exotic plant species in the natural ecosystem of Sitakunda Botanical Garden and Eco-park, Chittagong, Bangladesh through transect and random sampling and Focused Group Discussion (FGD) during August 2013 to April 2014. A total of 103 exotic plant species (99 species of angiosperms and 4 gymnosperms) belonging to 90 genera and 43 families were recorded through transect method from the study area. Among the exotics, tree species constitute the major category (46 species, 21 families) followed by shrubs (33 species, 18 families), herbs (21 species, 17 families) and climbers (3 species, 3 families). Mimosaceae family was represented by maximum (9) exotic plant species followed by Caesalpiniaceae (8), Myrtaceae (8) and Malvaceae (7). Most of the exotic plants were introduced in the eco-park after its establishment. Exotic tree species are given priority as the dominant plantation species in the eco-park area because of their short rotation, wider adaptability and faster growth. A total of 74 tree species (52 native and 22 exotic) belonging to 33 families were recorded through random sampling method in the eco-park. Number of both exotic and native tree species in hill top, mid hill and hill bottom varied simultaneously. Density of exotic trees were found maximum (366.6/ ha) in the hill bottom. Holarrhena antidysenterica (14.77) and Stereospermum colais (14.53) were the two native tree species that showed maximum Importance Value Index (IVI). Besides, two exotics that showed maximum IVI were Xylia xylocarpa (10.05) and Psidium guajava (9.15). The enumerated exotic plant species were categorized under six different traditional use categories according to their habit form (tree, shrub, herb and climber). The study revealed 39 exotic species used for timber purpose indicates their prominent economic potentiality. Moreover, local communities extracting exotic plants for meeting their needs of fuel, housing implements, livelihoods etc. Control of the exotics in future plantation programs need to be considered and available native plants should give priority to ensure ex-situ conservation of the Botanical Garden and Eco-park.