Rational　synthesis　of　photocatalytic　materials　is　an　effective　way　to　improve　their　performance.　In　this　work,　to　optimize　the　S　precursors,　a　series　of　MnxCd1−xS　(MCS)　were　first　hydrothermally　synthesized　with　the　prevalent　thiourea　(TA),　thioacetamide　(TAA)　and　L-cysteine　(L-Cys)　as　the　S　sources.　The　optimum　feed　ratio　of　Mn/Cd　was　then　determined　based　on　the　optimized　S　precursor.　The　effects　of　S　precursors　and　the　feed　ratio　of　Mn/Cd　on　the　phase　structure,　absorption,　morphology,　band　structure,　and　the　photocatalytic　hydrogen　evolution　reaction　(HER)　performance　of　MCS　were　investigated　systematically.　The　hexagonal　phase　structures　of　MnS,　CdS,　and　MCS　are　favored　by　TA　and　L-Cys　as　the　S　sources,　while　their　cubic　phases　are　benefited　by　TAA.　TAA　is　the　preferred　S　source　for　the　preparation　of　highly　active　MCS　and　the　solid　solution　is　formed　through　the　consolidation　of　cubic　α-MnS　into　cubic　CdS.　The　activity　of　MCS　can　be　improved　with　the　increase　of　Mn　content　from　x　=　0–0.6.　The　sample　with　x　=　0.6　shows　the　highest　HER　activity　(2253　μmol·h−1·g−1)　and　the　performance　is　almost　6　times　higher　than　CdS　(416　μmol·h−1·g−1).　The　enhanced　activity　can　be　attributed　to　the　improved　separation　efficiency　of　photo-induced　charge　carriers　and　the　negative-shifts　of　Ecb,　which　are　induced　by　the　introduction　of　Mn.　A　segregation　of　inert　α−MnS　from　MCS　is　occurred　when　Mn　content　is　＞0.6,　resulting　in　a　decay　of　the　HER　activity.　A　change　of　the　semiconductivity　from　n-type　to　bipolar　type　is　occurred　in　MCS　due　to　the　uneven　sulfidation　of　Mn　in　MCS.　©　2018