Urea formaldehyde/epoxy resin microcapsules were prepared by an in situ polymerization method and the effect of emulsifier on the syntheses process of the microcapsules was discussed.The surface morphology of the microcapsules was observed by optical microscopy and scanning electron microscopy(SEM).Chemical structure was characterized by Fourier transform infrared spectroscopy(FTIR).Thermal stability was obtained using simultaneous thermal analysis(STA).The microcapsules were composed of urea-formaldehyde resin shell and epoxy resin core.Emulsifier played an important role in the polymerization process when the core material was packed by pre-polymer,so the effects of different emulsifiers(OP-10,SDS and SDBS)were discussed respectively.Results showed that the particle size of the microcapsules was uniform when SDBS as an emulsifier.Microcapsules showed good thermal stability below 240 ℃ and the initial decomposition temperature of the microcapsules was 265 ℃.The core materials released after microcapsules rupturing,which could be proven by the images of SEM.When implanted in cementitious composites,complete shape of microcapsules and good interface between microcapsules and cement specimen substrate could also be observed.