The present invention provides a liquid preparation for oral administration that is capable of reducing the amount of colonic irrigation solution taken during gastrointestinal pretreatment and decreasing the burden on the subject without sacrificing test accuracy and without prolonging the time required for pretreatment, and a composition for gastrointestinal radiography used to prepare the liquid preparation for oral administration. Namely, provided are a liquid preparation for oral administration taken during gastrointestinal imaging by CT colonography that comprises an iodine compound and a water-soluble polymer or saline laxative, wherein 300 mL to 1200 mL are taken on the day before CT colonography in a single administration or divided among several administrations, and a composition for gastrointestinal radiography comprising an iodine compound and a water-soluble polymer or saline laxative, wherein 300 mL to 1200 mL are taken in the form of an aqueous solution, having an iodine content of 3.5 mg/mL to 90 mg/mL prepared by dissolving in water, on the day before CT colonography in a single administration or divided among several administrations.
