Abstract Biomass is seen as an alternative material to help reduce the dependency of fossil fuel usage in energy- and product-based application. In this thesis, the conversion of biomass, especially agricultural waste, to value added products through hydrothermal carbonisation (HTC) process were investigated. The aim of this research work is to deliver information on the suitability and practicality of the hydrothermal carbonisation process as an effective biomass conversion technology, in particular for palm oil wastes. The HTC process requires sub-critical water medium during the procedure to produce solid products (biocarbon) as the main products. Agricultural waste is classified as biomass material and normally generated in large quantity. In this work, two types of agricultural waste will be studied, which are palm oil empty fruit bunch (EFB) and wood chips (WC). The effects on the operating temperature, time and amount of water usage on the yield and carbon conversion for both materials were examined. A purpose built pressure vessel was designed, with the capacity to be operated up to 230°C and 30 bars. In addition, a program was constructed by using Lab VIEW software to control and record the operation. The characteristics of the biocarbon from EFB and WC were carried out through elemental, calorific, SEM, FTlR, pyconometer and RGB colour model, to examine the correspondence of the biocarbon characteristics with the operating conditions. The HTC process converts the EFB and WC into higher percentage of carbon content solid products. Based on these analyses, the increment of the operating temperature offer more improvement on the biocarbon quality compared to the residence time. The carbon conversion of EFB's biocarbon (operated at 220°C for 22 hours) increased for 20% compared to the raw EFB (43.8% of carbon). In addition, the calorific value of EFB's Abstract biocarbon increased from 17.7 to 28.2 Ml/kg, which is nearly similar with the value of lignite (26.8 MJlkg). A kinetic calculation of the process was calculated by combining the shrinking core model (SCM) and Arrhenius equation. The rate constant for both EFB and WC varies from 0.044 to 0.1 04s·l. Also, comparison on the economic calculation for direct combustion of EFB materials before and after the conversion process was carried out. Based on this calculation, it can be stated that the combustion process is not profitable for the HTC process' biocarbon because this process require quite a lot of energy. The usage of the biocarbon as plantation area was verified by using these products as soil conditioner in the radish growth starts and substrates in mushroom cultivation process. Finally, it can be conclude that the HTC process is practicable method to convert biomass into value added material. In future, improvement of the methodology such as an addition of catalyst in the process and agitator to the rig can be done to obtain higher yield. Also, depth investigations on the biocarbon behaviour in soil medium and effect on the growth and quality of plant is suggested. 11