Traditionally oilseed flax straw has been used for pulping and production of fine papers, mainly cigarette paper. But these markets only use a small percentage of total crop residue produced annually. The abundant availability of affordable natural fibres and shives in North America and the prospect of using them as biorenewable reinforcement in recycled plastics matrices have gained attention in recent years. This has resulted in more research, particularly in the application of natural fibre reinforced biocomposites derived from post consumer plastic materials. In this research a biocomposite board was developed using flax shives with a biopolymer binder made out of recycled plastic and flax fiber. Some advantages of such construction materials are high strength, low density, good insulation capacity against heat and moisture transfer, and biodegradability. Four binders based on pure and recycled HDPE (High Density Polyethylene) with two different percentages of flax fiber (as reinforcement to improve the mechanical and physical properties of the product) were assessed for flax shives to make biocomposite boards. Milk jugs were the source of recycled HDPE in these formulations. The flax fiber was chemically treated to improve the bond between the fiber and polymeric binder. The recycled plastic was also cleaned properly before processing. According to binder formulations, ingredients were mixed and extruded using a twin screw extruder. The extruded materials were ground and used as binder for flax shives at specific ratios. The biocomposite boards were manufactured by applying heat under compression. Some physical and mechanical properties of the bio-composite boards were also studied by performing ASTM tests viz., tensile and bending strength, melt flow index and water absorption.