PURPOSE: To obtain a urethane compound useful as a cross-linking agent for plastic uses or its intermediate by reacting a urethane, an aldehyde compound and an alcohol as raw materials in the presence of a solid acid catalyst in one stage.

CONSTITUTION: (A) A urethane having at least one H bound to N atom in the molecule, preferably that of the formula, R1-NH-COOR2 (R1 is H or a 1-8C hydrocarbon group; R2 is a 1-8C hydrocarbon group or may be connected to R1 to form an alkylene) is reacted with (B) an aldehyde compound of preferably the formula, R3CHO (R3 is a 1-6C hydrocarbon group) and (C) an alcohol of preferably the formula, ROH (R is a 1-10C hydrocarbon group, etc.) in the presence of (D) a solid acidic catalyst having preferably sulfonate and/or phosphate groups such as an acid type ion exchange resin or a zirconium phosphate to afford an N-(1-alkyloxyalkyl)-urethane. Furthermore, the components are preferably used at 1:(1.5-5):(2-10) molar ratio of the components (A):(B):(C).