To produce the subject polyurethane excellent in flame retardance and physical properties by reacting an active hydrogen compound partially containing a specific phosphorus compound having a hydroxyl group as a flame retardance-imparting component with a polyisocyanate.

This polyurethane is produced by reacting (B) an active hydrogen compound with (C) a polyisocyanate optionally in the presence of a catalyst, a foaming agent, a foam-controlling agent, etc. The component B contains at least partly (A) a compound obtained by esterifying (i) a polyhydroxy compound having at least two hydroxyl groups in a molecule with (ii) a phosphinic acid derivative of the formula (R1 is ethylene or 1,2-propylene; R2 is a 1-10C alkylene; R3 is a 1-10C alkyl, phenyl or an alkyl-substituted phenyl). The component A is preferably used at least 0.5wt.% in the polyurethane in terms of a phosphorus content.