For the proper use of micropowders in castables, slurries and fired samples were prepared with two kinds of corundum-spinel micropowders (D and G). The effects of the solid content and disperser WSM-R1 on the rheological properties of the slurries were studied. The sintering properties and the slag corrosion resistance of the fired samples were also researched. The results show that: the slurries all show pseudoplastic rheological characteristics. With the same solid content, the slurry with micropowder G has higher initial viscosity than that with micropowder D. Disperser WSM-R1 significantly reduces the initial viscosity of the two slurries and plays a more obvious dispersing effect on the slurry with micropowder G. The fired sample with micropowder G has higher bulk density, lower apparent porosity and better corrosion resistance than that with micropowder D.