With thiourea (Tu) as sulfur source and the assistance of CTAB, faceted and cubic Ag2S nanocrystals have been synthesized successfully via a simple hydrothermal route by modulating the ratio of Tu and AgNO3, respectively. It is the first report that the fabrication of faceted and cubic Ag2S nanocrystals takes place in aqueous medium, which makes the synthesis environmentally benign, user-friendly, economical and practicable to industry production. It is also found that the cooperation effect of CTAB and Tu should be responsible for the formation of the as-obtained Ag2S nanocrystals. The UV-vis absorption spectrum of the products shows obvious blue shift. (C) 2007 Elsevier Inc. All rights reserved.