Silicon ester dispersants were prepared using transesterification between ethyl petroleum silicate and the alkyl alcohols by different molecular masses. The dispersants were used to modify calcium carbonate (CaCO3), and their effect on the mechanical properties of CaCO3/polyethylene (PE) composites was investigated. The transesterification was confirmed by gas chromatography (GC). The optimal conditions for the preparation of silicon ester dispersants were 110 degrees C for 3 h with 2% catalyst by weight and fixed molar ratio of isooctyl alcohol to ethyl petroleum silicate of 3 : 1. Fourier transmission infrared spectroscopy (FTIR) results indicated that the dispersants were coating to the CaCO3 particles. Dispersant with octadecanol as its solvable chain enabled the best modification effect. CaCO3/PE composites modified by dispersants demonstrated improved mechanical properties. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2244-2249, 2010