A new microencapsulated flame retardant containing melamine polyphosphate (MPP) and 4,4'-Oxydianiline-formaldehyde (OF) resin as core and shell material was synthesized by in situ polymerization technology. The structures and properties of microencapsulated melamine polyphosphate (OFMPP) were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and water contact angle. Thermal behavior of OFMPP was systematically analyzed by thermogravimetric analysis. Flame retardant tests such as limiting oxygen index and UL-94 were employed to evaluate the effect of composition variation for the MPP and the OFMPP in polyurethane bridged polysilsesquioxane (Si-PU) composites. The results indicated that the microencapsulation of MPP with the OF resin led to an improvement of the hydrophobicity. Results also revealed that the flame retardancy of the Si-PU/OFMPP composite (LOI=32%) was better than that of the Si-PU/MPP composite (LOI=27%) at the same additive loading.