A system for recycling spent sulfuric acid, wherein spent sulfuric acid is effectively utilized at a place other than a discharge source regardless of geographical conditions, and a method for recycling waste sulfuric acid. In the system, when spent sulfuric acid that is discharged or collected at a discharge source is transported by a carrier unit and used at a user office a concentration of the spent sulfuric acid is measured and/or adjusted at least at one of the discharge source, the carrier unit, and the user office. The spent sulfuric acid waste liquid that is discharged or collected at the discharge source is reutilized by being mixed with at least one of a hydrogen peroxide solution and water.