Oil-containing microcapsules were prepared by using tolylene 2,4-diisocyanate (TDI) as an oil-soluble monomer and diethylene triamine (DETA) or lysine (LYS) as a water-soluble monomer. The diameter of the microcapsules decreased as the emulsifying time was increased within the initial period of three minutes, beyond which no appreciable changes in the diameter were observed. Once DETA was introduced into the aqueous solution to initiate the interfacial polycondensation reaction, reducing the stirring speed could diminish the formation of the membrane fragments, whereas the microcapsule diameter remained unchanged. When lysine was used as a water-soluble monomer, the zeta-potential of the TDI-LYS microcapsules was much higher than that of the TDI-DETA microcapsules. The mean diameter of the TDI-LYS microcapsules was smaller than that of the TDI-DETA microcapsules.