Cellulose diacetate (CDA)/kenaf fiber biocomposites were prepared using a melting process. In order to increase the fiber density and compatibilize the kenaf fiber with CDA, the fiber was sized with poly(vinyl alcohol)(PVA). The sized kenaf fiber was compounded with the plasticized CDA using a twin screw extruder, and the optimal processing conditions were determined. The incorporated kenaf fiber improved the mechanical and thermal properties of CDA. In the case of the composites containing 30 wt% kenaf fibers, the tensile strength and modulus increased almost 2 and 3 fold, which were 85.6 MPa and 4831 MPa, respectively. The PVA treated kenaf fiber showed better adhesion to the CDA matrix.