Abstract: An olefin polymerization catalyst is provided which makes use of a modified methylaluminoxane and thus stably exhibits an activity equivalent to, or higher than, the activity achieved by polymethylaluminoxane. Specifically, the olefin polymerization catalyst is in the form of a modified methylaluminoxane preparation prepared from: an organoaluminum compound represented by the following general formula (I): R1mAlX3-m??(I) wherein R1 represents a straight-chained or branched hydrocarbon group selected from the group consisting of alkyl, alkenyl, and aryl groups having 2 to 20 carbon atoms; X represents a hydrogen atom, halogen atom, alkoxy group, or allyloxy group; and 0<m?3; and trimethyl aluminum, wherein the mole fraction of methyl group of the aluminoxane unit with respect to the total number of moles of the hydrocarbon group having 2 to 20 carbon atoms and methyl group present in the modified methylaluminoxane preparation is 65 mol % or greater.

Abstract: An olefin polymerization catalyst is provided which makes use of a modified methylaluminoxane and thus stably exhibits an activity equivalent to, or higher than, the activity achieved by polymethylaluminoxane.