This article summarizes the investigation results of the rheological and thermal stability properties of industrially prepared wood plastic composites based on virgin polypropylene (PP) and birch plywood production waste product, plywood sanding dust (PSD). Wood plastic composites (WPCs) PP+40 wt.% PSD contain different modifiers, such as functional lubricant Struktol TWP, antioxidant 1010, thermal stabilizer 168, ultraviolet (UV) stabilizer 770, and pigment concentrate based on low density polyethylene (LDPE). According to these studies, it was concluded that rheological properties studied by the capillary rheometry method depend on WPC composition and the parameters of rheological measurements. On the contrary, melt flow index (MFI) values did not change so much and fluctuated in the range of 1.52–1.66 g/10 min. The presence of thermal and antioxidant stabilizers promoted an increase in the thermal stability of WPCs, as determined by the thermal gravimetric analysis (TGA) method. The characteristics of fluidity curves indicated the character of typical pseudo-plastic liquids, in which viscosity not only depends on temperature, shear stress, and shear deformation rate but also decreases with an increase in shear deformation rate. That also confirmed the values of the fluidity index (n), which for pseudo-plastic polymer melts are always smaller than 1.