Steel cleanness is an important and growing research area driven by the demands to produce high quality steel. Lowering the inclusion content in steel is an important criterion for clean steel. It is therefore important to better understand the interaction between inclusions and slag to improve the removability of inclusions from liquid steel. For efficient inclusion removal the inclusions must attach/bond with the slag phase. The strength of the attachment can be characterised by the wettability of the slag on the inclusions. In this study, the dynamic wetting of ladle slags of the CaO-Al2O3-SiO2- MgO system on a solid spinel (MgAl2O4) substrate was measured at 1500 degrees C using a modified sessile drop technique. The dynamic contact angle between liquid slag and solid spinel was determined for different CaO/Al2O3 mass percent ratios ranging from 1.02 to 1.52. Characteristic curves of wettability (0) versus time showed a rapid decrease in wetting in the first 10s tending to a plateau value at extended times. The chemical interaction at the interface between spinel (MgAl2O4) and slag was analysed by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS). There is evidence of interaction between the slag and the spinel at the substrate-slag interface and what appears to be erosion at the interface of up to 10 um into the substrate.