Wood-plastic composites (WPCs) represent a class of materials increasingly used in residential construction and furniture-making. The fire performance of WPCs is not well understood, however, and there is little information regarding the effectiveness of various fire retardants in the public domain. FPL scientists used oxygen index and cone calorimeter tests to characterize the fire performance of wood flour-polyethylene composites, and compared the results with unfilled polyethylene and solid wood. Five additive-type fire retardants were then evaluated for effectiveness on fire performance. Generally, magnesium hydroxide and ammonium polyphosphate improved the fire performance of WPCs the most while a bromine-based fire retardant and zinc borate improved fire performance the least. Manufacturers of WPCs can use this knowledge to improve the fire performance of their product and expand into new markets. WPCs consume under-valued woody biomass, increasing the production of WPCs will add value to biomass. This research was conducted as collaboration between scientists at FPL in the Engineered Composites Science research work unit and the Durability and Wood Protection research work unit and the University of Wisconsin-Madison Department of Mechanical Engineering.