Abstract: The flame retardant mechanism of the halogen- and phosphorus-free flame retardant melamine cyanurate (MC) on the epoxy resin by cured anhydride was investigated by means of limited oxygen index (LOI), thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the incorporation of MC into EP improved the flame retardancy. MC lowered the onset temperature and the maximum mass loss rate of EP on heating, and increased the thermal stability of EP at high temperatures(<400 ℃). But the condensed phase charring action of MC seemed to be poor. The flame retardant action of MC is mainly via heat sink in both the gaseous and condensed phases.