Using　the　hydrothermal　method,　a　P-doped　TiO2　nano-catalyst　is　prepared　for　widening　the　application　spectrum　of　TiO2.　The　synthesized　samples　are　investigated　using　XRD,　TEM,　and　UV-visible　absorption　spectra.　A　P-doped　TiO2　system　is　simulated　and　calculations　for　geometrical　structure,　electronic　and　optical　properties　are　performed　based　on　density　functional　theory.　Comparison　of　the　electronic　band　structure　of　anatase　TiO2　before　and　after　doping　verified　that　doping　tuned　the　band　structure.　XRD　patterns　revealed　that　pure　anatase　phase　is　the　only　phase　in　case　of　pure　and　doped　samples.　TEM　observations　reveal　spherical　morphology.　The　P　doped　TiO2　experimentally　as　well　as　theoretically　responded　to　visible　light　confirming　the　band　structure　findings.　Photocatalytic　activity　of　the　doped　samples　drastically　improved　compared　to　bare　TiO2.