To provide a method for forming a carbon-nitrogen bond, with which a reaction is advanced under a relatively mild condition by an inexpensive catalyst and an objective compound is mass-produced by a simple means.

An organic compound is reacted in the presence of a proton type montmorillonite catalyst to form a carbon-nitrogen bond. For example, a nitrogen atom-containing compound such as a sulfonamide, an acid amide, an amine, etc., is reacted with an unsaturated compound or an alcohol to form a carbon-nitrogen bond.