The effects of adding coal fly ash-derived zeolites on the physical properties of mortar such as compressive strength and voidage and on the repression of efflorescence by cation exchange were investigated. It was confirmed that efflorescence can be repressed by adding zeolites to mortar, and especially remarkable repression was observed when 10% or more of the Al-P (Al3+-containing zeolite P) was added. The main mechanism of the repression was thought to be the filler effect of zeolites on voids in mortar, suggesting that the movement of Na2SO4 solution in the mortar can be controlled by this effect.