Poly　(N-vinyl-2-pyrrolidone)-capped　CdS　nanocrystals　with　different　crystalline　sizes　were　synthesized　through　a　simple　solvothermal　method.　The　structures　of　the　as-synthesized　samples　were　characterized　by　XRD,　N-2　physisorption,　TEM,　IR　spectroscopy,　and　UV-Vis　spectroscopy.　The　results　show　that　the　as-synthesized　samples　are　poly　(N-vinyl-2-pyrrolidone)-capped　CdS　nanohybrid　materials;　the　grain　size　of　CdS　nanocrystals　is　smaller　when　tetramethylammonium　hydroxide(TMAH)　is　-introduced　in　the　reaction　system.　In　addition,　it　is　also　found　that　the　bandgap　of　CdS　nanocrystals　is　blue　shifted　and　the　visible-light　photocatalytic　activity　of　the　sample　synthesized　in　the　presence　of　TMAH　increases　due　to　the　size　effect.