In this study, the influence of wood fiber content (40, 50 and 60 wt.%) and coupling agent concentration (3 and 5 wt.%) on the mechanical properties of wood-plastic composites (WPCs) was investigated. Two types of plastic (high-density-polyethylene (HDPE) and recycled high-density-polyethylene (rHDPE)) were used as polymer matrices for preparing WPC. As reinforcement, prior grinded (fiber length < 0.5 mm) coniferous wood shavings were utilized. Overall trend showed, that by adding a wood fiber, flexural properties and microhardness of the composites significantly were enhanced. However, impact strength, water resistance, and fluidity of polymer melts decreased with increase in fiber content. The virgin HDPE-based composites as well as recycled HDPE-based composites, reinforced with fibers from coniferous wood, showed good mechanical properties. Based on the findings in this work, it appears that WPCs based on virgin HDPE, as well as on recycled HDPE, can be used to manufacture value-added panels. Optimal content of wood fibres were 50-60 wt.%.