In this report, doping concentration-dependent photoluminescence (PL) properties of Mn-doped ternary Zn-In-S quantum dots (QDs) were studied by using steady-state and time-resolved PL spectroscopy. The QDs PL was firstly significantly intensified with the increasing Mn doping concentration and then decreased after the doping concentration increased up to 7.5 at.%. However, their decay lifetimes exhibit a monotone decrease with Mn doping concentration ranged from 0 to 10 at.%. It can be concluded that the PL intensity was mainly determined by two factors: one was the increased efficiency of energy transfer from host excitons to Mn2+ ion accepter, and the other was the decreased efficiency of the emission from a Mn2+ ion, which was caused by the increased component of exposed Mn2+ ions on QDs surface and the accelerated interaction between adjacent dopants. The competition of above two exciton relaxation dynamics processes determined the trend of the PL intensity, while the latter was responsible for the monotonously decreased lifetime of the Mn2+ ion emission with the increasing Mn doping concentration.