Inclusion removal by slag is primarily achieved by optimizing process conditions that promote slag contact with the inclusion. For efficient inclusion removal the inclusions must adhere to 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 in the CaO-Al 2O3-SiO2-MgO system on spinel (MgAl 2O4) was measured at 1500°C using a modified sessile drop technique. The dynamic contact angle between liquid slag and solid spinel was determined for slags of two different mass percentage CaO/Al 2O3 (C/A) ratios, 1.25 and 1.55. Characteristic curves of wettability (θ) versus time showed a rapid decrease in the wetting angle in the first 10s tending to a plateau value at extended times. The plateau values for the %CaO/%Al2O3 ratio 1.25 and 1.55 slags were 16° and 19° respectively. Full details of experimental technique are reported and the wettability results of ladle slag systems with different C/A ratio are discussed.