Mn-doped ZnS nanocrystals were prepared by a co-precipitation method. X-ray diffraction analysis indicates pure cubic zinc blende structure. We report for the first time experimental observation of the dependence of the decay time of Mn2+ emission from Mn-doped ZnS nanocrystals on the photon energy of the excitation. Photon energy smaller than the ZnS bandgap induces the faster decay time compared to the one equal to the bandgap energy. In addition, while the decay spectra of orange emission indicate both sub ms and ms, the time-resolved luminescence measurement suggests that the sub ms component belongs to the tail of the blue emission.