We have discovered that nickel-complex-type organic nanotubes (Ni-ONTs) function as the catalyst for oxidation reactions of various organic compounds, indispensable for industries, in water at room temperature. Ni-ONTs were synthesized by the mass production method developed by AIST. Ni-ONT can be synthesized by the simple operation of mixing inexpensive an amphiphilic molecule, glycylglycine connected with a fatty acid, and nickel salt in solvents. Because all nickel ions are exposed on the inside and the outside surfaces of the nanotube, Ni-ONT is expected to provide excellent catalytic sites. Since Ni-ONT is solid in water, it can be easily recovered through filtration after catalytic reactions and is also recyclable. Therefore, Ni-ONT is expected to contribute to green innovation.