[Object] To improve bitterness or astringency, for example, to reduce stimulative bitterness or astringency of bitter or astringent food and drink, without imparting unnecessary taste or aroma to the food and drink.[Solution] A bitterness- or astringency-improving agent for bitter or astringent food and drink includes phthalides as an active ingredient. Addition of a very small amount of phthalides that are not sensed as aroma to food and drink improves undesirable bitterness or astringency of various bitter or astringent food and drink products and enhances or provides pleasant bitterness or astringency.