PURPOSE: To prepare a transparent compounded drug of vitamin B2 butyric acid ester for soft capsule, preservable extremely stably for a long period without forming precipitate, and having unparallelled high titer, by dissolving vitamin B2 butyric acid ester in free cholesterol.

CONSTITUTION: The titled drug can be prepared by dissolving vitamin B2 butyric acid ester in free cholesterol. Although vitamin B2 butyric acid ester has poor solubility in oils used as a drug component, the solubility can be improved remarkably by the addition of a compound having phenolic hydroxyl group, especially free cholesterol. A soft capsule of vitamin B2 butyric acid ester having unparallelled high titer, e.g. about 30mg/cap can be prepared by this process. It has no irritation to the oral mucosa and digestive tracts, is free from crystallization even at a low temperature, and can be stored extremely stably for a long period.