Composites based on birch plywood by-product: plywood sanding dust (PSD) and mixtures of virgin (vHDPE) and recycled high density polyethylenes (rHDPE) 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 usage of presented mixtures for preparing of qualitative WPCs containing 50 wt.% PSD. It was observed that the melt flow index values decrease with an increase of the content of rHDPE in polymer matrix. DSC measurements showed the diminishing of melting temperature and melting heat of vHDPE by adding of rHDPE. The tensile strength and modulus of composites decrease about 25 – 30 % but frexural strength and modulus have no changes. In the contrary impact strength and microhardness of the samples increased with an increase of additives of rHDPE. Water uptake kinetics of all composites were similar and the total amount of absorbed water after 850 h of the soaking was 12 – 13 %. The optimal content of recycled HDPE in the composites could be 25 – 30 wt.%. In general presented studies showed successful possibilities of the use of additives of rHDPE to vHDPE to produce cheaper WPCs which have no worse guality. Moreover the chosen type of rHDPE in the some cases can compete with investigated vHDPE matrix.