Model tests were performed in order to obtain collapse behavior of TSUKIISHIBU section in masonry walls under long-term load; the TSUKIISHIBU section represents the whole part of the masonry wall structure excluding corner. A wall model was constructed by rectangular prism shaped masonry stones placed one on another with initial angle of slope on dry sand backfill, and the angle of slope was increased quasi-statically until the model collapses. It is observed that when the initial angle of slope is steep the model collapses with overturning mode of the wall and when the initial angle of slope is relatively mild the model collapses as if the wall was bending at the middle height. As wall heights that the model collapse show good agreement with critical slope curves those are theoretically obtained, validity of the theory for predicting critical height of the wall is clarified.