PURPOSE: To obtain the titled compound useful as drugs, agricultural chemicals, fluorescent substances, etc., at relatively low temperature by one stage in high yield, by reacting a nitrile with anthranilic acid or an ester or an amide derivative thereof as inexpensive raw materials in the presence of an alcohol under low pressure.

CONSTITUTION: A nitrile (e.g. trimethylacetonitrile, etc.) shown by the formula R1CN (R is alkyl, aryl, aralkyl or heterocyclic group) is reacted with anthranilic acid shown by formula I (R2 is R1, H, halogen, nitro or OH; R3 is OH, alkoxy or amino) or a derivative (e.g. methyl anthranilate, etc.) in the presence of an alcohol (preferably alcohol) under pressure about 1,000W9,000 atm at 20W150°C (relatively low temperature not to cause side reaction) to give a quinazolin-4-one [e.g.; 2-(t-butyl)-quinazolin-4-one, etc.] shown by formula II.