The homopolymerisation of styrene is studied in the presence of Y, USY and beta zeolites. High molecular weight polymers, in the range 0.7 x 10(6)-1 x 10(6), are obtained in good yields. The activity of zeolite beta is only slightly increased by calcination of the as-synthesised material, pointing to an important role of the zeolite outer surface. The influence of the catalyst acidity upon the polymer molecular weight is evaluated by the use of dealuminated zeolites.