The　growth　of　trace　amount　of　niobium　(Nb)　doped　beta-Ga2O3　thin　films　have　been　demonstrated　on　(0001)　sapphire　substrates　by　radio　frequency　magnetron　co-sputtering　method.　The　crystallization,　morphology　and　optical　properties　of　Nb　doped　beta-Ga2O3　films　have　been　investigated.　The　deep　ultraviolet　(DUV)　photodetector　with　a　metal-semiconductor-metal　structure　based　on　trace　amount　of　Nb　doped　beta-Ga2O3　thin　film　was　fabricated.　The　DUV　photodetector　exhibits　high　photo-to-dark-current　ratio　and　fast　photo-response　speed,　suggesting　the　performance　of　beta-Ga2O3　photodetector　can　be　improved　by　doping　trace　amount　of　Nb　in　beta-Ga2O3　thin　film.