PROBLEM TO BE SOLVED: To provide a better dementia-improving agent that is effective in each patient.SOLUTION: An effective dementia-improving agent can be provided for each of the persons in which the content ratio of docosahexaenoic acid to total fatty acid in serum is high or low by providing a dementia-improving agent containing Yokukansankachimpihange as an active ingredient for persons in which the content ratio of docosahexaenoic acid to total fatty acid in serum is high and by providing a dementia-improving agent containing Yokukansankachimpihange and docosahexaenoic acid as an active ingredient for persons in which the content ratio of docosahexaenoic acid to total fatty acid in serum is low.