Microcapsules were prepared by in situ polymerization of melamine-formaldehyde resin to form shell over oxygen resin droplets. Stirring rate, temperature, pH value as well as mass ratio of shell and core are the main parameters affecting the stability of microcapsules. High stirring rate leads to small size of microcapsules. The temperature influences the speed of the reaction and the morphology. The pH value decides whether the condensation reaction can take place. The size of microcapsules is about 15-61um.