The paper describes the conversion of blast furnace slag to glass-ceramics by the casting route as well as investigating the microstructure of the crystalline phases on the basis of XRD, DTA and SEM. The effect of particle size on the crystallization behavior of the slag-derived glass was studied by DTA at different particle size. X-ray Diffraction indicates the presence of gehlenite (Ca2Al2SiO7), BaAl2Si2O8 and pyroxene Ca(Mg,Al)(Si,Al)(2)O-6. Crystallization has been showed to be slightly varied with particle size, indicating a bulk crystallization mechanism The bulk glass and glass-ceramic were also evaluated by Vickers microhardness.