The present study aimed to characterize plant community structure of rubber plantations abandoned 26 years previously and now a protected area of Prince of Songkla University on the west slope of Kho-Hong Hill. Trees whose girth at breast high were at least 30 cm were recorded from thirty-one plots (10*10 m) which were laid out systematically at every 100 m along three transects. Among native trees, this plant community is dominated by Schima wallichii Choisy, Castanopsis schefferiana Hance, Memecylon edule Roxb., Diospyros frutescens Blume, and Diplospora malaccensis Hook.f. Trees of the families Myrtaceae, Theaceae, Clusiaceae, Fagaceae, and Rubiaceae, and saplings of Clusiaceae, Myrtaceae, Theaceae, Rubiaceae and Euphorbiaceae were the most common. This plant community was characterized as a late seral stage post-cultivation succession. The basal area of rubber trees was positively significantly related to the species richness of native trees but negatively related to the density of native trees in each plot. Although abandoned rubber plantations create environmental conditions which effectively catalyze forest succession, dense rubber trees could slow succession of native trees by competition for resources. Further ecological, educational and recreational studies are discussed. Zoning this area to be a strict nature reserve and a conservation area is recommended.