A composition containing 1,4-dihydroxy-2-naphthoic acid at a high concentration is obtained by intracellularly and extracellularly producing 1,4-dihydroxy-2-naphthoic acid using a bacterium belonging to the genus Propionibacterium and collecting it. This composition is efficacious in improving intestinal flora, alleviating abdominal ailments in association with the intake of milk, and preventing metabolic bone diseases.