Wood-plastic composites (WPCs) are very promising and sustainable green materials to achieve durability without using toxic chemicals. These materials, produced by blending biopolymers and natural fillers, permit us not only to tailor the desired properties of materials according to the characteristics and ratios of wood and polymers but are also the solution to meet environmental and sustainability requirements. This study focuses on the durability evaluation of green WPCs made from a blend of an entirely biodegradable biopolymer (BIOPLAST GS2189 supplied by Biotec-Germany) and spruce wood sawdust. The spruce sawdust with different amounts (from 0 to 30% weight) was introduced into Bioplast and the obtained blends were injected into injection molds in order to manufacture the samples, which are eco-friendly materials and biodegradable in specific conditions. To determine the biological resistance of the produced WPCs, the decay and termite resistance tests, conducted according to screening tests adapted from European Standards, were carried out in relation to the wood content. The results showed an increase in fungal and termite degradation levels with increasing amounts of wood in Bioplast. It also showed a relationship between the water uptake due to fungi growth and a decrease in the resistance against fungal and termites. The optical microscopy observations performed on WPC specimen surfaces highlighted the presence of microcracks on the surface of WPCs after their decay exposure, resulting in an embrittlement of the composite containing high wood content. These observations were discussed in order to understand the pathways of degradation mechanisms in these WPCs. Although Bioplast partial substitution by wood decreased the resistance of WPCs to fungal and termite attacks, the elaborated WPCs in this study were still in the class of strongly durable material.