Magnetic properties of the initial (pre-milling) and mechanically activated SmMnO3 polycrystalline powders were studied. Magnetization measurements were carried out in the temperature range of T = 4-300 K and the magnetic fields up to +/- 20 kOe. The powders were subjected to both high-energy and low-energy ball milling. The samples studied were analyzed by X-ray diffraction method and X-ray photon-emission spectroscopy. It was found that all the mechanically activated powders SmMnO3 have significantly different magnetic characteristics (transition temperatures, coercive forces, remanent magnetizations) in comparison with initial samarium manganite. The inversion of field cooled (FC) and zero-field cooled magnetizations was observed for the initial sample only. Mechanically activated samples demonstrate positive FC magnetizations in the whole measured temperature range. It is established that the magnetic properties of the samples are strongly dependent on the mode of mechanical activation. Much noticeably, modifications in magnetic characteristics of powder studied were obtained in the case of low-energy mechanical treatment.