The hydraulic potential stimulation of magnesium is significant to its direct utilization. In this paper, magnesium slag which is the main material, and some slag and activator are used to prepare cementitious material and bricks, and the influences of different activators on the hydraulic properties are also investigated. Experiments show a certain hydraulic potential of magnesium slag but with a low strength, however, the compressive strength soars from 1.8 MPa to 27 MPa after composing it with a small amount of blast-furnace slag. The early strength of magnesium slag-blastfurnace slag binder is affected by NaOH, while the gypsum affects the binder’s later strength. Bricks conforming to standard MU20 are successfully fabricated by 80% magnesium and 20% blast furnace slag, after activated, with extra 5% desulfurized gypsum.