One type of birch wood plywood by-product: plywood sanding dust (PSD) and recycled high density polyethylene (rHDPE) composites physical mechanical properties (tensile, flexural strength and modulus, impact strength and microhardness), water resistance and fluidity of the composite melts, were evaluated. These studies showed the possibility of the usage of presented byproduct as an excellent reinforcement for recycled high density polyethylene matrix. It was observed that the modulus of the tensile for unmodified rHDPE+PSD composites increased up to 2.3 times, the modulus of flexural till 4 times, but the microhardness only 1.4 times. Optimal content of the PSD in recycled high density polyethylene composites could be 50 wt.%. As a coupling agent, the maleated polyethylene (MAPE) for modifying of the rHDPE + 50 wt.% PSD composite was used. Due to the MAPE additives, the improvement (30 – 50 %) of the investigated exploitation properties was observed, but in comparison with unmodified composites the resistance of water increased up to 3.0 times. Optimal content of MAPE in rHDPE + 50 wt.% PSD composition could be 3 wt.%