In steel foundries, ceramic filters are often used to capture non-metallic inclusions. It is well documented that solid inclusions are captured and retained within the filter macropores at the metal-refractory interface. However, liquid inclusions appear to be captured and retained by two mechanisms: one within the filter web micropore structure and another as a liquid film at the metal-filter macropore interface. Experiments were carried out to study the removal of various non-metallic liquid inclusions by magnesia-stabilized zirconia filters. The results documented the effective removal of liquid inclusions in all experiments. Samples were extracted from filter element to investigate the inclusion attachment mechanism during deep bed filtration. Energy-dispersive X-ray spectroscopy and associated scanning electron microscopy was employed to evaluate the inclusion attachment mechanism with the ceramic filters. Liquid inclusion retention in the filter micropores followed an exponential trend from entry to exit side of the filter, until the micropores became completely saturated. After complete saturation, the retained inclusion distribution remained constant through the thickness of the filter. Filters were found to capture the liquid inclusions, drawing them into the open micropores due to inclusion-refractory favorable wetting conditions. Once the accessible micropores were fully saturated, liquid inclusion films developed at the metal-filter macropore interface, increasing the possibility for the release of large liquid inclusions from the filter.