The present invention provides a process for producing a 4(3H)-quinazolinone derivative, which is useful as a medicinal substance, with better efficiency in an industrial scale. The process comprises the steps of reacting 4-hydroxy-N-tert-butoxycarbonylpiperidine with 4-fluoro-1-nitrobenzene in the presence of sodium hydride, reacting the resulting product with cyclobutanone, reducing the resulting product to give 4-(1-cyclobutyl-4-piperidinyl)oxyaniline, and reacting this compound with 2-methyl-5-trifluoromethyl-4H-3,1-benzoxazin-4-one to give 3-{4-[(1-cyclobutyl-4-piperidinyl)oxy]phenyl}-2-methyl-5-trifluoromethyl-- 4(3H)-quinazolinone.