Conserving carbon density of tropical peat swamp forest is an important indicator of environmental and agronomical impact of oil palm. Understanding the carbon stock contribution from management within oil palm areas to retain forest patches and other set-asides containing natural forest may become increasingly important in the context of assessing the potential contribution to the global carbon cycle and one of the most critical strategies for sustainable plantation. However, quantification of carbon stock of tropical peat swamp forest patches for conservation within oil palm plantations is poorly studied. Here, we aim to assess the above-ground biomass and flora diversity in a remnant forest patch of approximately 210.63 ha adjacent to oil palm plantation. Two 1 ha Tinbarap Conservation Forest (TCF1 and TCF2) study sites were established to conduct census on all trees (≥10 cm diameter breast height). The total carbon stock of both TCF sites was 92.6 mg ha-1. The TCF contains flora from 27 families comprising 69 species. Conserving forest patches, particularly in peatlands, is important for conservation goals and sustainable palm oil industry.