A study was conducted in a semi-deciduous forest at the Perlis State Park, Perlis, Peninsular Malaysia, to determine floristic composition, diversity and structure of tree communities in three forest habitats of the State Park. The three habitats are characterized of different geological formations, viz. Setul Formation, Kubang Pasu Formation and Granite. Eight plots (1.92 ha) of 40 m x 60 m each, were established in Setul, six plots (1.44 ha) were set in Kubang Pasu and four plots (0.96 ha) in Granite, totaling a sampling area of 4.32 ha. All trees with diameter of 5 cm and above were enumerated in all the study plots. A total of 4300 trees were recorded that comprised of 412 species, 207 genera and 68 families. Euphorbiaceae was the most speciose family in all three habitats, represented with 36 species at Setul, 12 species at Kubang Pasu and 19 species at Granite. Leguminosae, Anacardiaceae and Moraceae were the most important families in Setul, Granite and Kubang Pasu habitats, respectively. At species level, Saraca cauliflora (Leguminosae) was the most important species in Setul, while Swintonia floribunda (Anacardiaceae) and Pentaspadon curtisii (Anacardiaceae) were the most important species in respective habitats of Granite and Kubang Pasu. Diversity wise, the Shannon diversity index (H’) showed varied index values where the Setul showed the highest diversity index of 4.60, followed by Granite (H’=4.40) and Kubang Pasu (H’=3.60). Seventy eight tree species were listed in the IUCN Red List of Threatened Species with various categories that include critically endangered, endangered and vulnerable. As a whole, the flora of the Perlis State Park is a characteristic of limestone flora of a semi-deciduous forest.