Lead sulfide nanocrystals have been prepared by two novel routes in microwave heating and ultrasonic irradiation. In the experiments, lead acetate and thiourea are used as lead source and sulfur source, respectively. Different size and morphology of lead sulfide (PbS) nanocrystals can be obtained by using ethanol, distilled water, ethylene glycol and polyethylene glycol-200 as solvents. X-ray diffraction results show that the as-prepared PbS nanocrystals have a cubic structure. Probable mechanisms for the formation of PbS particles are also proposed. (C) 2004 Elsevier B.V. All rights reserved.