Provided are: a liquid preparation for oral administration, which contains barium that can be mixed with residues readily and is rarely precipitated in the intestinal tract and a liquid preparation for oral administration and a composition for imaging the digestive tract, each of which contains barium and enables the reduction of the dosage of an intestinal tract washing solution in a pretreatment of the intestinal tract. That is, provided are: a liquid preparation for oral administration, which comprises barium and at least one thickening agent selected from the group consisting of a naturally-occurring polysaccharide and a cellulose-type polymer, and has a viscosity of 100 mPa·s or more at a shear rate of 21.54 s-1 and 5 to 90 mPa·s at a shear rate of 464.1 s-1, wherein barium has such a volume cumulative distribution that the particle diameter D10 is 0.30 to 0.80 μm and the particle diameter D90 is 1.0 to 10 μm and a liquid preparation for oral administration for use in the imaging of the digestive tract by CT colonography, which comprises barium and a water-soluble polymer or a salt-type purgative agent and is to be administered in an amount of 50 to 2000 mL in a single dose or several divided doses on the day before carrying out the CT colonography.
