Single-crystal KCaSrTa5O15 nanorods were successfully synthesized by a polymerized complex method. SEM and TEM observations revealed that the nanorods growing along the c axis of a tungsten bronze structure measured 40100 nm in diameter and 100300 nm in length. Tb(0.03 atom%)-doped KCaSrTa5O15 nanorods gave a green luminescence due to the 5D4 → 7F6 and 5D4 → 7F5 transition of Tb3+, when the KCaSrTa5O15 host was excited. The intensity of the luminescence was much higher than that by polycrystalline KCaSrTa5O15 prepared by a solid-state reaction. This indicates that nonradiative deactivation at grain boundaries was suppressed in the KCaSrTa5O15 nanorods compared to the polycrystalline KCaSrTa5O15. NiO cocatalyst-loaded KCaSrTa5O15 nanorods split water into H2 and O2 with an apparent quantum yield of 6.6% at 254 nm. The efficiency was three times as high as that of the polycrystalline KCaSrTa5O15. The KCaSrTa5O15 nanorods also showed photocatalytic activity for CO2 reduction, when a Ag-cocatalyst was loaded. Stoichiometric amounts of CO and H2 as reduction products and O2 as an oxidation product were obtained. The activity for CO2 reduction was improved by adding NaHCO3 into the reactant solution, giving about 90% CO selectivity (CO/ (CO + H2)).