High energy ball milling (BM) of micro H-Y zeolites was studied at a wide range of speeds, milling duration, and ball sizes. SEM analysis reveals that BM produces three types of species that can be distinguished namely: nanoparticles, flakes/slabs, and un-ground micro-sized particles. BM at high speeds reduces the particle size of zeolite to the nanometer range in a very short duration. However, BM for longer time led to the formation of zeolite flakes. The particle size reduction was achieved at the cost of loss in zeolite crystallinity. Among several combinations of BM processing parameters, BM at 1000 rpm for short duration were found to be the optimum parameters to reduce the zeolite into nanoparticles while retaining considerable crystallinity. Post BM centrifugation was found to be essential in obtaining a homogeneous particle size distribution. The produced nanoparticles had an average diameter of 50-100 nm, surface area of 465 m(2)/g, and a crystallinity index of 20%.