Strength properties of Wood Plastic-bonded Boards (WPBB) of 10mm in thickness were produced in this study from two lignocellulosic materials coffee and recycled low density polyethylene (rLDPE) as a binder. WPBB were produced from particles of coffee chaff and Ceiba pentandra, at three levels of mixing ratio (1:1, 2:1 and 3:1), and at three levels of board density (500, 600 and 700kgm-3 ) given the total treatment combinations of 18 respectively. Effects of lignocelluloses particles, mixing ratio (MR) and board density (BD) on flexural strength properties of the WPBB were investigated. The flexural strength of the WPBB range from 0.25 to 4.79N/mm2 and 891.00 to 16415.87N/mm2 for modulus of rupture (MOR) and modulus of elasticity (MOE) respectively. The statistically results shows that the main factor and interaction factors were significantly different at P≤0.05 level of probability. It was observed in this study that as the plastic content with density increased, flexural strength of the boards increases. The study showed that WPBB made from coffee chaff particles are stiffer and stronger than WPBBs made from Ceiba pentandra particles. Based on the outcome of the results in this study, coffee chaff could as well be used as filler in the polymer industry to produce stronger biopolymer composite for structural applications. This study would form a baseline strategy for further research efforts on production of composite from agro-residues wastes.