The instant invention relates to a composition and process for the stabilization of halogen containing polymer slurries, in particular polyvinylchloride (PVC). The composition comprises a halogen containing polymer in the form of an aqueous suspension or emulsion, a partially hindered phenolic antioxidant and selected sulfur containing antioxidants, which are both solid at 20° C. A further aspect of the invention is the use of specific antioxidant mixtures for the stabilization of halogen containing polymer suspensions or emulsions, in particular PVC.