This dataset presents peat soil data from the Badas peat swamp forest in Brunei Darussalam, focusing on ash content and elemental compositions to understand fire impacts. Peat samples were collected from two transects established in 2017, with 11 and 14 sampling points, respectively. Cores were extracted to a depth of 150 cm, combined into 12 fractions, and analyzed for ash content and elemental concentrations. Ash content was determined using oven-drying and muffle furnace ashing methods. Elemental analyses for Al, Ca, Fe, and Mg were conducted using acid digestion followed by ICP-AES analysis. The dataset, comprising 300 samples each for ash content and elemental concentrations, provides valuable insights into fire-induced changes in tropical peatlands.