The authors have been developing low-rise reinforced concrete masonry buildings with the wall thickness of 150mm, for the purpose of the increase of inner space of buildings, the decrease of building weight, and the usage of the standard building module of 300mm. In order to realize the buildings, compressive behaviors of fully grouted concrete masonry prisms, using newly developed small-size units with the strength of 40N/mm² class and grout concrete of the strength of 40-60N/mm², were investigated. Special pre-mixed cement mortal was used for the joints to obtain high out-of-plane bending performance.