Polyurea microcapsules were prepared by interfacial polycondensation using diisocyanates as the oil soluble monomers and diethylenetriamine as the water soluble monomer. NP-10, nonionic surfactant, was used as an emulsifier. Toluene was used as the diluent of the diisocyanates as well as the means to prepare microcapsule with empty shell. Number average particle size of the microcapsule showed a linear relationship with the viscosity of the dispersed oil phase. Polyurea microcapsule with thinner shell thickness showed good thermal stability well above $250^{circ}C$ and showed same thermal stability compared to that with thicker shell thickness.