A method of the intramolecular and intermolecular cyclization of an N-acylhydrazone for obtaining a pyrazoline skeleton or pyrazolidine skeleton under ordinary conditions with high stereoselectivity and in high yield. An N-acylhydrazone represented by the following formula (I): (wherein R1 and R2 are the same or different and each represents hydrogen or a hydrocarbon group and Ar represents an optionally substituted aromatic hydrocarbon group) is converted to an N-acylpyrazoline derivative with high stereoselectivity in the presence of a Lewis acid catalyst or asymmetric Lewis acid catalyst.