Ga　and/or　N　doped　TiO2　nanoparticles　synthesized　by　one　pot　hydrothermal　method　possess　pure　anatase　phase　with　spherical　morphology.　Calculations　based　on　density　functional　theory　(DFT)　explained　the　band　gap　narrowing,　origin　of　optical　absorption　and　the　possible　changes　in　the　photocatalytic　activity　of　synthesized　nanophotocatalysts.　Analysis　of　band　structure　and　density　of　states　revealed　that　N　and　Ga,　N　codoping　introduced　some　partially　occupied　states　above　the　valance　band　maximum　which　might　influence　the　electron　hole　pair　recombination.　Calculations　as　well　as　experiments　confirmed　the　shifting　of　absorption　edge　towards　visible　regime　due　to　doping.　Spectroscopic　investigations　confirmed　the　existence　of　dopant　atoms　in　the　doped　samples.　Ga　doped　TiO2　samples　provided　the　best　photocatalytic　activity　compared　to　the　synthesized　samples　attributed　to　the　suitable　band　structure,　enhanced　optical　absorption　and　effective　separation　between　photoexcited　carriers.