Abstract: In order to study the effect of mortar strength on compressive behaviors of grouted concrete masonry, nine specimens using lime mortar were analyzed. According to failure pattern, cracking load, ultimate capacity and deformation capacity, a formula was provided to calculate the compressive capacity of grouted concrete masonry when the mortar strength is very low. The ratio of cracking load to ultimate load is very small, which affects the durability of masonry building. Therefore, this paper states that the mortar strength should be higher than a critical value when designing and constructing grouted concrete masonry.