By utilizing a Confocal Scanning Laser Microsope, the wettability as well as penetration behaviors of coal and petcoke slags on high chromia and alumina refractories have been investigated. The petcoke slag showed the lower initial deformation temperature and also lower melting temperature than the coal slag. The high chromia refractory, in general, returned better corrosionlerosion resistance against both slags with the exception that the alumina substrate outperformed in minimizing the slag penetration when the petcoke slag was interacted with a fined region of the refractory. The VONx-based phase was observed as a layer of (V, Cr, Fe)Ox at the interface between the petcoke slag and the high chromia substrate; and as discrete particles of (V, Al, Si)Ox at the interface between the petcoke slag and the alumina refractory. In some cases, Ca- and Fe-rich VOx, was also observed. For the coal slag, Ca-species penetrated most slowly through the fined regions of both refractories, whereas Fe-species was the fastest in any case.