Waste concrete is usually caused to recover its ingredients, and is then divided into a coarse fraction, while contains mainly the coarse aggregate, and a fine fraction, which consists of a mixture of hydrated cement and aggregate fragments. Waste concrete powder (WCP), we studied, contained more than $40\%$ of insoluble ingredients, while its chemical composition appeared similar to that of cement. Containing cement hydration products which include capillary pores, the specific gravity of the WCP was in the range of $2.4~2.6$. Flow value of fresh mortar with WCP was reduced due to pores within the hydration products absorbing the mixture water, and it is difficult to measure the flow value of mortar containing WCP $30\%$. Compressive and flexural strength at 7 and 28 days of mortar with WCP were smaller than those of the control mortar without the WCP, because to the dehydraed cement within the WCP. In addition, the compressive and flexural strength of the mortar containing the WCPl $30\%$ appeared to be reduced $32\%;and;15\%$ 28days compared to the mortar with only cement, respectively.