Orthorhombic (orth.) SrTa2O6 powder which was hardly obtained by a solid state reaction was easily synthesized by using a strontium borate flux. The native SrTa2O6 powder showed photoluminescence and a photocatalytic activity for decomposition of pure water into H2 and O2. The photocatalytic activity was drastically increased by loading a NiO co-catalyst even without pretreatment. The optimum amount of NiO loaded was 0.10 wt%. The quantum yield of the NiO(0.10 wt%)/SrTa2O6 photocatalyst was 7% at least.