Phase Change Materials (PCMs) have attracted growing attention recently in the renewable energy utilization and building energy efficiency due to their high capacity for storing thermal energy but their applications have been restricted by leakage, poor thermal conductivity, and high flammability. In this work, the flame retardant phase change material has been successfully prepared through integrating Resorcinol bis (diphenyl phosphate) (RDP) as a flame retardant into lauric acid (LA) as a phase change material. The DSC (differential scanning calorimeter) test is used to measure the thermal properties of LA_RDP. The thermogravimetric analysis (TGA) test demonstrates that the thermal stability of composite LA_RDP is improved. Cone calorimeter is applied to study the flammability properties of the flame retardant phase change material. As a result, the RDP-based flame-retardant PCMs developed could be used for safe and efficient solar energy storage applications.