To make an intestinal tract-cleaning agent containing magnesium citrate for a pretreatment of barium enema X-ray inspection or large intestine-endoscopic inspection, be easily swallowable to enhance the acceptability towards subjects.

This intestinal pre-treatment cleaning agent used for the pre-treatment of the barium enema X-ray inspection, the endoscopic large intestine inspection and an abdominal surgery is provided by adding a thickening agent to an isotonic or hypertonic magnesium citrate liquid.