Abstract: This study focuses on flame retardanting effects of dimethyl methylphosphonate (DMMP) and Al(OH)3 as two reprehensive types of organic and inorganic halogenfree flame retardants. The experimental results indicated that the flameretardant effect of DMMP is more effective than that of Al(OH)3 when being used alone. A combination of the organic and inorganic flame retardants could generate a gradient synergistic effect on flame retardancy when the mass ratio of DMMP and Al(OH)3 was set to 4:2. The resulting flameretardant polyurethane foam achieved an oxygen index of 28.5 %, and its thermal stability was much better than that of pristine polyurethane foam.