Red phosphorus (RP) was used to improve the fire performance of wood flour - low density polyethylene (LDPE) composites containing ammonium polyphosphate (APP). The fire performance of LDPE-based composites was investigated by using limiting oxygen index (LOI), UL-94 standard, thermogravimetric analysis, and cone calorimeter. The addition of 30 wt% APP increased the LOI value from 17.5 to 24.2 and still burned to clamp (BC) in UL-94 test. The RP showed beneficial effect when combinedly used with APP. The maximum beneficial effect was seen at ratio of 5: 1 (APP : RP) with the highest LOI value of 27.2 and UL-94 rating of V0. RP showed its beneficial effect via increasing the gas phase action of the flame retardant system. Copyright (C) 2015 John Wiley & Sons, Ltd.