This paper explains that granulated blast furnace slag sand can improve the resistance of concrete to sulphuric acid attack. When a part of cement is replaced with ground granulated blast furnace slag, and the granulated blast furnace slag sand is used for sand, the resistance of concrete to sulphuric acid attack can be improved because a coating of gypsum (calcium sulfate dihydrate) is formed on the mortar or concrete. A coating of gypsum is strong enough to prevent the corrosion caused by sulphuric acid attack. The relationships between the immersed depth of mortar or concrete by sulphuric acid attack and the product of soaking time and concentration of sulphuric acid are liner. This paper will show that the resistance to sulphuric acid attack of concrete with granulated blast furnace slag sand is 6 times higher than that of ordinary concrete. The exposure test on sulphuric acid in the sewer for one year has been done, and the superiority of concrete with granulated blast furnace slag sand has been confirmed.