PURPOSE: To obtain wall membranes of capsules having solvent resistance by causing a polyvalent isocyanate compd. to react in hydrophilic liquid dissolved with PVA denatured by sulfonic groups.

CONSTITUTION: After hydrophobic liquid contg. polyvalent isocyanate is emulsified and dispersed in hydrophilic liquid dissolved with PVA denatured with sulfonic groups, synthetic high polymer membranes are formed at the oil-water interface to enclose the surfaces of the hydrophobic liquid drops, whereby microcapsules are produced. The resultant microcapsules are highly resistant to heat and moisture and is highly resistant to solvents as well.