Environmental and economic factors are increasingly encouraging higher value utilization for waste concrete. The use of recycled aggregate as replacement of natural aggregate for the production of concrete structures has become increasingly popular in the concrete construction industry. However, the use of the recycled aggregate is very limited because recycled aggregate which contains large amount of old mortar has very low quality. Therefore, removing the old mortar recycled aggregate is very important. This experimental study is to remove the ingredient of old cement paste from recycled fine aggregate using the acid treatment as chemical processes, and investigates the engineering properties of the mortar using it. Test results indicate that recycled fine aggregate by acid treatment process satisfies the quality standards for the first-grade recycled fine aggregate of KS F 2573. It is also shown that the properties of recycled fine aggregate by acid treat are superior to those of natural fine aggregate. However, the properties of mortar using recycled fine aggregate by sulfuric acid treat was inferior to those of natural water treat.