Mn-doped ZnO diluted magnetic semiconductor nanoparticles are prepared by an ultrasonic assisted solgel process. Transmission electron microscopy shows pseudo-hexagonal nanoparticles with an average size of about 24 nm. From the analysis of X-ray diffraction,the Mn-doped ZnO nanoparticles are identified to be a wurtzite structure without any impurity phases. The magnetic properties are measured by using superconducting quantum interference device. For the ZnO with 2 % Mn doping concentration, a good hysteresis loop indicates fine ferromagnetism with a Curie temperature higher than 350 K.