This study was conducted to investigate the effect of liming and fertilizer application on mineralization of nitrogen in hemic and sapric peat material of Tropical Histosols. The peat materials were left to decompose aerobically for 8 weeks under laboratory incubation and samples were taken for extractable ammonium at every 1 week interval. The trends in nitrogen mineralization were found to be similar between hemic and sapric peat materials for all treatments; however the rate and amount of ammonium release differed. The application of lime increased the pH of the peat material from around 3.7 to a pH of about 6.0 but no significant differences were found in the amount of NH₄⁺ at 8 weeks of incubation between treatments with and without liming material in hemic and sapric peat material respectively. Fertilizer application significantly increased NH₄⁺ in both peat materials, where NH₄⁺ in hemic material was significantly higher (23.85 g/kg) compared to sapric (16.48 g/kg) peat material. This study showed that the practice of liming to increase soil pH did not necessarily improve the mineralization of nitrogen in Hemic and Sapric peat therefore was not prerequisite unless the crops to be planted are intolerant to acidity.