Abstract: A mixture of aluminum hydroxide (ATH) and magnesium hydroxide (MH) was microencapsulated by melamineformaldehyde (MF) by insitu polymerization under alkaline condition. The product（MMA）was characterized by Fourier transform infrared spectrometer (FTIR), scanning electron microscope (SEM) and thermogravimetry (TG). The flammability and mechanical properties were evaluated using limiting oxygen index test and universal testing machine, respectively. FTIR showed that the bands from 1600 to 1300 cm-1 assigned to the MF emerged in MMA. SEM indicated that MF had an effect on the growth of MA crystals, and the particle diameter reduced in MMA. The limiting oxygen index and mechanic property testing showed that MMA possessed improved flame retardacy and better mechanical property than MA.