Copyrolysis of biomass is one of the potential options to improve the quality of bio-oil. In this study, different types of feedstock, palm empty fruit bunches fiber (EFBF) and palm oil mill effluent (POME) sludge, were conducted via thermogravimetric analysis. The,Thermogravimetric behavior of EFBF and POME sludge blends (EFBF:POME sludge mass ratio of 100, 90, 75, 50, 25, and 0%) were subjected to different heating rates of (5, 10, 20, 30, 40 degrees C/min) with a nitrogen (N-2) purge of 20 riaL/min to-simulate pyrolysis conditions. As the percentage of POME sludge in the blend increases, the thermogravimetric data and thermogravimetric derivative profiles shifted from EFBF to that of POME sludge gradually. A higher mass loss rate of EFBF upon devolatilization indicates the higher reaativity,than that of POME sludge. During copyrolysis, a positive synergistic effect was observed All the samples, experienced three pyrolysis stages, and for each stage, the mechanisms responsible were determined. The third order kinetic Model (F3) was identified as the most suitable model in-the Master-plot method. However, a deviation from the theoretical master plot at high percentage, of POME sludge in blends was observed. Therefore, a stagewise analysis of copyrolysis was done,using the Coats-Redfern (CR), method. A change in diffusion mechanism was identified as POME sludge percentage increased in blends during the.main "decomposition stage, which reveals the lack of a specific shape for sludge particles.