A Ni-Mo sulfide bed occurs in the lower portion of the lower Cambrian Niutitang Formation in south China. Lehmann et al.(2007) reported data of Mo-isotopic compositions of the Ni-mo sulfide ores and host black shales, and suggested aseawater origin for the Mo. The Ni-Mo sulfide ores show very limitedMo-isotopic variation with δ98/95MoMOMOvalues of -1.24‰±0.10‰, whereas the host black hales show larger Mo-isotopic variations with δ98/95MoMOMO values from ～1.82‰ to－0.40‰. Those with low-Mo content black shales show a linear relationship between Mo contents and Mo-isotopic compositions. We suggest that this correlation may reflect a two end-member mixing of seawater Mo and clastic sedimentMo. The sources of Mo in the Ni_Mo sulfide ores were probably from submarine hydrothermal fluids. Further work is needed both on the Ni-Mo ore bed bearing and the barren black shales of the Niutitang Formation in south China, in order to better estimate the Mo-isotopic compositions of the early Cambrian seawater, and to better constrain the ore genesis.