This　work　spotlights　the　formation　behavior　of　visible　light-responsive　tantalum　oxynitride　(TaON)　thin　film　photocatalysts　under　high　substrate　temperature　in　radiofrequency　reactive　magnetron　sputtering　deposition.　The　results　emanating　from　the　optimization　of　the　sputtering　conditions　demonstrated　that　sputtered　N　atoms　with　high　kinetic　energy　generated　by　controlling　target-substrate　distances　and　total　pressures　in　the　sputtering　chamber　were　necessary　to　grow　TaON　phase　even　under　N-2-rich　atmosphere.　Based　on　these　findings,　TaON　thin　film　photocatalysts　were　successfully　synthesized　by　single-step　sputtering　under　a　high　substrate　temperature　of　1073　K　before　heat　treatment.　The　optimal　thickness　of　TaON　thin　film　photocatalysts　was　extrapolated　to　be　450　nm　by　photoelectrochemical　measurements　under　visible　light　irradiation　(lambda　＞　450　nm),　in　which　distinct　photocurrents　corresponding　to　water　oxidation　were　observed.　Moreover,　the　photoelectrochemical　activity　was　able　to　be　improved　by　postsynthetic　heat　treatment　in　gaseous　NH3　and　loading　with　IrO2　nanocolloids　as　cocatalysts.　This　finding　would　be　because　the　thin　film　photocatalyst　after　heat　treatment　in　NH3　under　appropriate　conditions　possessed　better　crystallinity　and　moderate　donor　density.　The　optimized　TaON　thin　film　photocatalysts　with　IrO2　nanocolloids　also　exhibited　photocatalytic　activity　for　H-2　evolution　from　aqueous　medium　containing　methanol　as　a　sacrificial　electron　donor　under　visible　light　irradiation　(lambda　＞　450　nm).