In this paper, the properties of inter­locking block using fly ash are discussed in order to provide economical advantages and improve quality, and protect environment and recycle resources. Fly ash is the by-product of coal in thermal power plant. The experimental parameters are fly ash content, the amount of AE water­reducing agent and mixing proportion of cement mortar. According to the experimental results, the improvement of quality in the side of strength, absorption ratio and freeze­thaw resistance for manufacturing inter­locking block and the curtailment of cost can be achieved in case of 15% of fly ash and 0.3% of AE water- reducing agent are mixed into mortar mixture of 1:6(C:S).