The　La3+-doped　TiO2　photocatalyst　was　prepared　by　the　improved　sol-gel　and　impregnation　method.　XRD,　N-2　adsorption,　UV-Vis　diffuse　reflection　spectroscopy　and　surface　photovoltage　spectroscopy　(SPS)　were　applied　to　study　the　effect　of　La3+　doping.　At　the　same　time,　the　photocatalytic　process　of　TiO2　and　La3+-doped　TiO2　catalysts　for　degradation　of　ethylene,　acetone,　benzene　were　further　studied　by　means　of　in　situ　FTIR.　The　result　indicated　that　La3+　doping　could　enhance　the　photocatalytic　activities　of　ethylene,　acetone,　benzene　to　some　extend　as　compared　with　pure　TiO2.　The　increase　in　photoactivity　is　probably　due　to　higher　content　of　anatase,　smaller　particle　size,　higher　specific　surface　area　and　lager　band　gap.　In　addition,　the　higher　photocatalytic　activity　of　La3+-doped　TiO2　may　be　attributed　to　the　stronger　photovoltage　signal　and　the　effective　separation　of　photo-generated　electron-hole　pairs.　The　result　also　showed　that　ethylene　could　be　photocatalytic　ally　oxidized　to　CO2.　The　acetone　and　benzene　may　be　photocatalytically　oxidized　to　propionic　acid　and　phenol,　quinone,　respectively.