Abstract The effects of the polypropylene-grafted maleic anhydride (PP-g-MAH) and polypropylene methyl polyhedral oligomeric silsesquioxane (PP-POSS) compatibilizers on the mechanical, thermal and physical properties of palm kernel shell (PKS) reinforced polypropylene (PP) were investigated. The production of PP/PKS biocomposites was performed by melt mixing using Brabender Internal Mixer. Mechanical test results showed that the biocomposites with PP-g-MAH have better tensile strength compared to biocomposites with or without PP-POSS. The results also showed an increase in the tensile strength and elongation at break when compatibilizers were added. Polypropylene-grafted maleic anhydride improved the Young’s modulus of the biocomposites, but PP-POSS reduced it. Moreoever, adding compatibilizers in biocomposites reduced the water absorption of the biocomposites. The compatibilizers improved the nucleating ability of filler in the composites. The PP-g-MAH compatibilizer provided better performance in improving nucleating ability to biocomposites compared to PP-POSS.