Abstract: Melamine-formaldehyde (MF) resin microcapsules containing resoreinol bis (diphenylphosphate)（RDP）were prepared by in situ polymerization. RDP acted as the core material and MF resins as the wall material. The effects of surfactant and prepolymer on the physical properties of melamine–formaldehyde encapsulated RDP microcapsules were investigated. Chemical structure of the prepared microcapsules was characterized by X-ray photoelectron spectroscopy (XPS). Morphologies and thermal properties were also investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TG). The results showed that the mixed surfactant had well distributed and uniform particles，and a size of 40—80μm. When the mass ratio of prepolymer and RDP was 1∶1，the micro-capsule size was minimum，with little melamine resin deposited on the surface.The results indicated that the initial thermal decomposition temperature of microcapsule increased from 400℃ for original RDP to 800℃，showing better thermal stability.