This study explored the floristic composition, diversity and biomass in Gunung Inas Forest Reserve (GIFR), Kedah, an area facing potential threats from large-scale monoculture durian plantations. Three 0.53 ha plots were established to assess trees with a diameter at breast height ≥ 5 cm. As a result, a total of 53 individuals were identified, representing 16 species, 16 genera and 12 families. The Shannon-Weiner Diversity Index was recorded at H’=2.77 and Margalef’s Richness Index at DMG=8.7, indicating low level of diversity and richness of tree in the forest. Moderate Evenness Index of E=0.71 portrayed the almost equal distribution of the tree species in the forest. Anacardiaceae had the highest FIVi at 24.79 % while Swintonia schewenkii was the most important species with SIVi = 12.48. Total tree biomass was estimated at 76.3 t/ha which was contributed by 66.04 t/ha and 10.22 t/ha of above ground biomass and below ground biomass, respectively. Furthermore, the study identified 2 of the 16 recorded tree species within the study area as threatened, highlighting the potential conservation concerns within this ecosystem. Overall, this study provides baseline data for future ecological research and calls for conservation efforts to protect this forest's biodiversity against potential threats.