This study aims to investigate the effects of two types of wood flour; oil palm mesocarp flour (OMF) and rubberwood flour (RWF), and their particle sizes on mechanical, physical, and thermal properties of wood flour reinforced recycled polypropylene (rPP) composites. The composite materials were manufactured into panels by using a twin-screw extruder. The rPP composites based on RWF significantly showed higher flexural, tensile, and compressive properties (both strength and modulus) as well as hardness and thermal stability than those composites based on OMF for the same particle sizes. However, distribution of RWF in the rPP matrix was less homogeneous than that of the rPP/OMF composites. Furthermore, a decrease of the particle sizes of filler for the rPP/OMF or RWF composites increased the flexural, tensile, compressive, and hardness properties. Likewise, the thermal stability of both OMF and RWF composites were insignificantly affected by the particle sizes.