Canadian grown oilseed flax is known for its oils that are used for industrial products. The flax fiber may also have a use as a potential replacement for synthetic fibers as reinforcement in plastic composites. It can also be utilized as a cost effective and environmentally acceptable supplement in the biodegradable composites. Tire rubber is a complex material which does not decompose naturally. As a result, many researchers have been trying to develop new applications for recycling scrap tires. The conversion of flax straw and scrap tire into a profitable product may benefit the agricultural economy, tire recycling market, and our environment. The main goal of this research was to develop a biocomposite material containing recycled ground tire rubber (GTR), untreated flax fiber, and linear low-density polyethylene (LLDPE).<p> In this study, the new biocomposite material was successfully prepared from flax fiber/shives, GTR, and LLDPE through extrusion and compression molding processes. The composites were compounded through a single-screw extruder. Then the pelletized extrudates were hot pressed into the final biocomposites. The properties of the flax fiber-GTR-LLDPE biocomposites were defined by using tearing, tensile, water absorption, hardness, and differential scanning calorimetry (DSC) tests. The effects of the independent variables (flax fiber content and GTR-LLDPE ratio) on each of the dependent variables (tear strength from tearing test, tensile yield strength and Youngs modulus from tensile test, and weight increase from water absorption test) were modeled. The properties of the composites can be predicted by using the mathematical model with known flax fiber content and GTR-LLDPE ratio.<p> The tensile yield strength and stiffness of the biocomposite were improved with the addition of flax fiber. The optimal composition of the biocomposite material (with strongest tensile yield strength or highest Youngs modulus) was calculated by using the model equations. The maximum yield strength was found to exist for a flax fiber content of 10.7% in weight and GTR-LLDPE ratio of one. The largest Youngs modulus was found for a fiber content of 17.7% by weight and the same GTR-LLDPE ratio. Both of these fiber contents were less than the amount that would give a composite with a 2% weight increase in water absorption.