For elucidating the validity of accelerated Ca leaching tests, the chemical and physical changes of a hardened ordinary Portland cement induced by the leaching into deionized water were compared with those induced by the accelerate leachings with proton-type cation exchange resin for the continuous elimination of Ca²⁺, with an electrostatic electric field for the electrophoretic elimination of Ca²⁺, and with NH₄NO₃ solutions for the elimination of OH⁻. The use of the resin and the electrostatic field were found to be inappropriate because both the methods caused the formation of strong acid which severely attacked and etched the paste. The use of a NH₄NO₃ solution was an appropriate method for the accelerated test, since Ca²⁺ was homogeneously leached in the paste and the amount of the leaching was controllable by properly selecting the concentration and the volume of the NH₄NO₃ solution.