PROBLEM TO BE SOLVED: To provide a polyurethane resin for a water-equivalent phantom material, which has high water equivalence, excellent mechanical strength, and excellent flexibility.SOLUTION: The polyurethane resin for a water-equivalent phantom material is obtained by reacting a polyurethane resin-forming composition containing a polyol, a polyisocyanate, and an organic filler and has an electron density of 3.20×10-3.50×10electrons/cm. A molded article for a water-equivalent phantom material is obtained by molding the resin. The density of the molded article is preferably 0.95-1.05 g/cm.