[en] The microstructure and magnetic properties have been investigated systematically for Sn_1-xMn_xO₂ (0 ≤ x ≤ 7%) nanoparticles synthesized by chemical co-precipitation method. The X-ray diffraction reveals that all samples are pure rutile-type tetragonal phase and the cell parameters a and c decrease monotonously with the increase of Mn content, indicated that Mn ions substitute into the lattice of SnO₂. X-ray photoelectron suggests that Mn ions behave as the mixture state of Mn³⁺ and Mn⁴⁺ in samples. Magnetic investigations demonstrate that magnetic properties strongly depend on both the sintering temperature and doping content. No ferromagnetism is observed for samples sintered at high temperature (T_S = 800 deg. C), irrespective of the doping content. In contrast, the samples sintered at low temperature (T_S = 450 deg. C) possess room temperature ferromagnetism when the doping content is below 5%. A plausible explanation of the magnetic properties is presented in terms of bound magnetic polaron model