A novel method for the preparation of sphalrite-type HgS (beta -HgS) nanocrystals by microwave irradiation is reported in this paper. Mercury acetate and thiourea were used as mercury source and sulfur source, respectively. It was found that the HgS with different average crystal sizes from 8 to 23 nm were obtained by using different solvents. The products were characterized by powder X-ray diffraction, transmission electron microscopy, electron diffraction, X-ray photoelectron spectroscopy, energy-disperseive X-ray analysis and UV-Visible absorption spectroscopy. The probable mechanism of the formation of beta -HgS nanocrystal is discussed.