PURPOSE: To obtain an isocyanate trimerizing and urethane forming catalyst highly active under a relatively mild condition by using cesium fluoride or tetrafluoroalkyl ammonium.

CONSTITUTION: As an isocyanate trimerizing catalyst or an urethane forming catalyst, cesium fluoride or tetrafluoroalkyl ammonium is used. This catalyst is reacted with isocyanate having a substituted or non-substituted alkyl or aryl group, substituted or non-substituted monofunctional or polyfunctional straight chain or branched alcohol or a substituted or non-substituted aromatic compound having a hydroxyl group in a solventless state or in an aprotic polar solvent. This catalyst advances the trimerization of isocyanate and the formation of urethane in a highly selective manner under a mild condition.