Abstract: The process of the present invention uses an aminoaldehyde polycondensate as capsule-wall and a hydrophobic core material dispersed in an aqueous acidic solution containing an anionic water-soluble colloidal substance, wherein it is characterized in that the anionic water-soluble colloidal substance comprises a mixture of an anionic water-soluble substance having a high viscosity and that having a low viscosity.The process of the present invention provides a slight viscosity rise in the encapsulation, a capsule slurry with a high concentration, low viscosity, and a slight smudging in the application as a pressure-sensitive recording sheet and the like, compared with the conventional processes.