A　color　medical　image　enhancement　algorithm　has　been　developed.　A　histogram　equalization　was　first　applied　to　the　saturation　component　in　color　difference(C-Y)　color　space,　then　the　histogram　modification　to　luminance　was　achieved　by　taking　into　account　the　relationship　that　exited　between　luminance　and　saturation　and　the　luminance　value　limitations　of　the　range　of　possible　saturations　in　color　images,　so　it　reduced　unrealizable　color.　The　new　algorithm　has　been　applied　to　medical　color　ophthalmologic　images,　the　experimental　results　showed　that　this　algorithm　is　effective.