NiS2-xSex solid solution has been successfully prepared via an ultrasonic solvothermal route. The products were characterized by X-ray diffraction, ICP-AES and X-ray photoelectron spectroscopy. It has been found that the lattice parameter a follows a Vegard law with the selenium content x(Se). The effects of ultrasonic and solvent on synthesizing NiS2-xSex solid solution were discussed. By comparing the Se molar fraction in the reagents to the selenium content in the samples, the formation mechanism of NiS2-xSex solid solution was proposed. Scanning electron microscopy images indicate that the products exhibit different morphologies corresponding to different compositions. (C) 2002 Elsevier Science B.V. All rights reserved.