The morphology and properties of blends of PP/HDPE and MAPP/HDPE blends, and their composites with wood powder, were investigated in this paper. The blends showed two-phase morphologies, and MAPP interacted better than PP with HDPE, while the WP interacted more strongly with MAPP. Although the different components in the blends were immiscible, they showed one crystallization peak. MAPP and HDPE showed separate crystallization peaks in the composites, and this separation of the crystallization became more resolved with increasing WP content and at lower cooling rates. This was also observed for PP and HDPE in their composites, but to a lesser extent. Young’s modulus increased and the stress at break decreased with increasing WP content, and these were more pronounced in the PP/HDPE/WP composites. Interaction between WP and MAPP also had an influence on elongation at break. The presence of WP increased the thermal stability of the MAPP/HDPE and PP/HDPE.