Molybdenum　sulfide　(MoSx)　is　a　prevalent　photocatalytic　and　electrocatalytic　material,　attributed　to　its　highly　active　unsaturated　sites.　Despite　that,　its　intrinsic　activity　is　still　under　expectation　for　large-scale　hydrogen　evolution　reaction　(HER).　Though　the　incorporation　of　Co-promotor　could　further　promote　MoSx　activity,　a　tedious　preparation　is　required　due　to　the　incompatible　properties　of　Co　and　Mo.　Herein,　we　report　a　facile　one-step　precipitation　of　cobalt-modified　amorphous　molybdenum　sulfide　(Co-MoSx)　cocatalyst　while　focusing　on　its　promotional　effects　to　ZnCdS　at　λ　＞　420　nm　region.　Co-MoSx　at　different　Co/Mo　ratios　were　photochemically-anchored　on　ZnCdS　support　through　an　in-situ　light-induced　reduction　at　ambient　conditions.　In　particular,　ZnCdS/Co-MoSx　(Co/Mo　=　1/4,　1　mol%)　was　emerged　as　the　best　formulated　photocatalyst,　with　HER　rate　and　apparent　quantum　efficiency　(AQE)　of　551.48　μmol　h−1　and　21.7%　(420　nm),　respectively.　While　reducing　the　overpotential　for　HER,　Co-modification　could　also　facilitate　the　separation　of　photogenerated　electrons　and　holes　for　the　enhanced　HER.　Therefore,　the　reported　HER　rate　of　ZnCdS/Co-MoSx　is　in　superior　to　that　of　ZnCdS/MoSx　and　pristine　ZnCdS,　by　1.4　times　and　23　times,　respectively.　Meanwhile,　similar　ascendency　of　Co-MoSx　was　also　observed　in　its　comparison　against　the　benchmarked　Pt,　Au　and　Ag　co-catalysts.　Additionally,　the　recycling　test　evinced　the　satisfactory　stability　of　ZnCdS/Co-MoSx　catalyst,　with　a　slightly　reduced　activity　observed　after　25　h　consecutive　HER,　marking　an　average　STH　of　1.4%　under　AM　1.5G　solar　simulator.　This　work　provides　a　facile　way　to　synthesis　Co-modified　MoSx　co-catalyst　that　rendered　with　excellent　properties　for　efficient　HER.　©　2021　Elsevier　B.V.