FIELD: stabilization of polymers. SUBSTANCE: invention, in particular, relates to composition containing calcium or magnesium acetylacetonate and at least one beta-diketone in free form and/or in metal chelate form with melting temperature below or equal to 200 C, weight ratio of components ranging from 1:10 to 10:1, preferably from 1:6 to 6:1. Invention also provides method for preparing such composition and using it in a process of formation of polymer composition containing halogenated polymer. EFFECT: considerably improved homogeneity of calcium or magnesium acetylacetonate dispersion and thereby improved dispersing of composition. 8 cl, 2 ex
