Abstract: The possibility of applying the laterite nickel ore smelting slag as the admixture of cement is analyzed. The result shows that the slag radioactivity and leaching toxicity are far lower than the limit value of national standard，without any hazards. The slag belongs to the common industrial waste solid and can be used as the raw building materials that not affect the product quality. It has potential hydraulic property with qualified pozzolanic property，and it can be used as active admixture. After stabilizing treatment，the cement mixed with the slag has a qualified autoclave expansion. The cement-mortar strength gradually decreased with the increasing of the slag content. SEM images and XRD patterns of the specimens of cement pastes without the slag and mixing with 30% slag at 28 d are analyzed，and the reason for affecting the property of the specimens of cement pastes is pointed out.

Key words: Laterite nickel ore, Smelting slag, Cement admixture, Leaching toxicity, Autoclave expansion