This paper deals with the effect of the electric furnace slag sand on the strength of cement mortar cured in ordinary and steam conditions. The strength of cement mortar using slag sand is developed more than that used Toyoura standard sand at age of all days. Also, the slag sand treated with 0.5% H_2SO_4 or 1% NaOH solution is more effective for develoment of mortar strength. It has been shown that the sand crushed from electric furnace slag is useful for mortar and concreat.