Microencapsulation of mono-dispersed stable kerosine droplets was carried out by complex coacervation of gelatin and acacia and the effect of operating condition on the membrane thickness of generated capsule is investigated. Mono-dispersed kerosine droplets were prepared using a porous glass membrane with narrow pore distribution. We succeeded in excluding the complicated influence of emulsification of core material on microencapsulation and in investigating the effect of operating conditions of the encapsulation process on capsule morphology separately by the use of mono-dispersed droplets as the core material. The drop size distribution and stability of the kerosine emulsion prepared by membrane emulsification were measured. The shape of the capsule is influenced sensitively by surfactant concentration and stirring rate. The number of cores included in a capsule increases, as the amount of kerosine increases.