ZnS　microspheres　self-assembling　from　ZnS　nanocrystals　were　synthesized　via　hydrothermal　treatment　at　low　temperature.　L-cysteine(an　ordinary　amino　acid)　was　used　as　a　sulfur　source　and　gelatin(an　ordinary　amino　acid)　was　used　as　the　assembling　agent.　By　combining　the　results　of　XRD,　TEM,　FESEM,　FTIR,　it　was　found　that　gelatin,　reaction　time　and　temperature　all　played　key　roles　in　the　formation　of　ZnS　spheres.　The　photocatalytic　activity　of　ZnS　samples　had　been　tested　by　degradation　of　Rhodamine-B　(RB)　under　UV　light.　Comparing　with　ZnS　crystals　synthesized　without　gelatin,　ZnS　microspheres　synthesized　with　gelatin　showed　better　photocatalytic　performance.　PL　spectrum　confirmed　that　the　photocatalytic　performance　of　the　as-synthesized　ZnS　spheres　is　related　to　their　high　content　of　sulfur　vacancies.