The　Gd3+-doped　TiO2　photocatalyst　was　prepared　by　the　sol-gel　and　impregnation　method.　The　effect　of　Gd3+　doping　on　crystalline　size,　BET　surface　area　and　photocatalytic　activity　was　studied　by　XRD,　FTIR,　BET,　UV-Vis　diffuse　reflection　spectroscopy,　surface　photovoltage　spectroscopy　(SPS).　The　activities　of　TiO2　and　Gd3+-doped　TiO2　catalysts　for　photocatalytic　degradation　of　ethylene　were　studied　by　means　of　in　situ　FTIR.　The　photocatalytic　reaction　rate　constant　of　ethylene　becomes　larger　through　Gd3+　doping.　The　rate　constant　of　TiO2　was　k(1)=8.51　x　10(-4)　min(-1),　while　that　of　Gd/TiO2　was　k(2)=1.85x10(-3)　min(-1).　At　the　same　time,　the　yield　of　CO2　increased　with　Gd3+　doping.　The　enhancement　in　photocatalytic　activity　is　probably　due　to　the　increase　of　light　absorption,　higher　content　of　anatase,　smaller　crystal　line　size　and　higher　specific　surface　area.　In　addition,　the　higher　photocatalytic　activity　of　Gd3+-doped　TiO2　might　be　attributed　to　the　effective　separation　of　photo-generated　electron-hole　pairs.