The influence of the nano-zinc oxide amount was evaluated relative to the flammability behavior, as well as the morphological and mechanical properties of wood plastic composites (WPCs). The polymer amount was approximately 50 wt%, and the lignocellulose material was 50 wt%. Nano-zinc oxide was applied at six weight levels including, zero (control), 1, 2, 3, 4, and 5 phc. For all treatments, the maleic anhydride polyethylene (MAPE) amount was 2 phc. The WPCs were made using a mixture of nano zinc oxide, high-density polyethylene, and mixed hardwood flour injection molding method. The morphological and mechanical properties, such as flexural strength and modulus, were measured. Various tests were conducted with a cone calorimeter, including the amount of char residue, total smoke production, time to ignition, and heat release rate, according to ASTM E1354-92 (1992). The flexural strength and modulus of composites in samples with 5 phc nano-zinc oxide were 79.9% and 27.2% greater, respectively, than in samples without nano zinc oxide. Nano-zinc oxide enhancement to 5 phc increased the ignition time and char residue 105.1% and 121.7%, respectively, and decreased the burning rate and total amount of smoke production 20.3% and 46.0%, respectively. Scanning electron microscope results indicated the presence of nano-zinc oxide agglomerates in the sample.