Manganese alloy slag is an industrial waste produced from manufacture of manganese alloy. Recent years environment pollution of manganese slag has been becoming heavier and heavier with the development of manganese industry. Aiming to sort out this problem, combination of manganese slag and ground granulated blastfurnace slag (GGBS) were applied to prepare alkaliactivated cementitious material. Compressive strength and flexural strength of cementitious material prepared with combination of alkalislagmanganese slag were measured. And microstructure of hydration production was investigated by scanning electromicroscope (SEM). It was shown that the flexural and compressive strength of cementitious material with alkaliGGBSmanganese slag system were decreased with the increase of replacement of GGBS by manganese slag. The increase of the fineness of manganese slag was favorable for strength improvement of the alkaliGGBSmanganese slag material. It was concluded that ground manganese slag had hydraulic activity in alkaliactivated cementitious material and the activity was lower than that of GGBS.