Processing of highly filled suspensions like ceramic in polymer matrix intended for injection molding or extrusion require specific properties, like a proper flow behavior and a good dispersion, that are often difficult to obtain in a first approach. The key is generally to control the particles-matrix’ interface of the filled suspension, which is both a must and a challenge to reach the target properties. A simple method is here described to characterize and optimize the filler surface chemistry in the case of zirconia filled polymeric suspensions using stearic acid as a surfactant. It involves contact angle measurements by the sessile drop method between water and thermally treated zirconia powders mixed with stearic acid. It is shown that this is a powerful way to determine the optimum additive concentration. In addition, the effect of partially coated particles on the dynamic rheological behavior of the molten filled suspension is investigated. Besides, the kinetics of the hydrophobization of the powder surface is followed by contact angle measurements and can be a way to improve the powder preparation.