The　effect　of　dolomite　with　different　particle　size　fractions　on　hematite　flotation　was　studied　using　sodium　oleate　as　collector　at　pH　of　about　9.　The　effect　mechanism　of　dolomite　on　hematite　flotation　was　investigated　by　means　of　solution　chemistry,　ultraviolet　spectrophotometry　(UV),　inductively　coupled　plasma　atomic　emission　spectrometry　(ICP-AES)　and　X-ray　photoelectron　spectroscopy　(XPS).　It　is　observed　that　dolomite　with　different　size　fractions　has　depressing　effect　on　hematite　flotation　using　sodium　oleate　as　collector,　and　dolomite　could　be　the　＂mineral　depressant＂　of　hematite　using　sodium　oleate　as　collector.　The　reasons　for　that　are　concerned　with　sodium　oleate　consumption　and　the　adsorption　onto　hematite　of　dissolved　species　of　dolomite.