PURPOSE: To obtain an aminopolysiloxane-based polymer excellent in release properties and useful for elastic parts, etc., by reacting an organic polyisocyanate with a specific aminopolysiloxane and a crosslinking agent.

CONSTITUTION: An organic polyisocyanate such as p-phenylene diisocyanate is reacted with an active hydrogen-containing main component comprising an aminopolysiloxane having a number average molecular weight of 1,500 or more, the active hydrogens derived from the aminopolysiloxanebing being more than 50% of the active hydrogens reacting with the polyisocyanate from active hydrogen-containing components having a molecular weight of more 1,000 and an active hydrogen-containing crosslinking agent to obtain a desired polymer.