We describe a new, green, and cheap route to the preparation of zinc sulfide nanocrystals at moderate temperature open to air in noncoordinating solvent paraffin liquid. The as-prepared ZnS nanocrystals with average size 4.7 nm presented particular UV-vis absorption. Cubic crystal lattice structures with good crystallization are characterized. A mechanism of ZnS nanocrystals formed in paraffin liquid as well as other similar solvent is demonstrated.