A Hungarian natural zeolite was mechanically activated by grinding in a Netzsch MiniCer stirred media mill for various activation times from 0 to 480 min. The research goal was to produce submicron-size activated zeolite with narrow particle size distribution and to investigate the energetic aspects of grinding and material characteristics. During mechanical activation (MA) the grinding energy was measured and stress energy was calculated. Additionally, the particle size distribution of the product was characterized by a Horiba 950 LA laser particle size analyzer (LPSA). Furthermore, the BET specific surface area and adsorption capacity of the MA zeolite were measured using TriStar 3000 apparatus and methylene blue adsorption test, respectively. The structural characterization of mechanically activated zeolite was carried out using Rietveld refinement on X-ray powder diffractometry data, Fourier transform infrared spectroscopy and transmission electron microscopy (TEM-EDS). TEM images and LPSA data of MA zeolite revealed the presence of particles below 100 nm. Significant amorphization, as well as the decrease in clinoptilolite phase, was found during entire MA process, while methylene blue adsorption was maintained. Finally, the relationship between grinding operating parameter (specific grinding energy) and material characteristics (amorphous content, the crystallite size of quartz and clinoptilolite) was created.