This study explores the mechanical, thermal and morphological properties of untreated and cyanoethyl-treated kempas wood sawdust cellulose fiber-reinforced unsaturated polyester composites. The fiber loadings of the composites were varied from 0 to 20wt%, with the increment of 5wt%. The composites were tested for water absorption, and their FTIR spectroscopy, SEM and TGA results were analyzed. The FTIR results show that the fiber treatment reduces the hydroxyl groups in the cellulose, replacing them with the cyanoethyl groups. The TGA results show that the composites are stable up to 324 degrees C. SEM images of the treated fiber composites showed that there were no visible gaps between fibers and matrix which indicates a strong interfacial bond. From the mechanical tests, 15wt% fiber loading composite was strongest. Among all the composites, cyanoethyl cellulose fiber unsaturated polyester composites had the most desirable mechanical and thermal properties, whereas the fiber treatment showed the improvement of interfacial bonding.