Photometathesis of propene over siliceous mesoporous silica, FSM-16, was revealed to be a novel type metathesis system consisting of two photoexcitation steps. For both steps, photoirradiation is essential, but the effective wavelength for each step is different: UV light is necessary for the first step, while visible light as well as UV light is effective for the second step. In the first step, photoabsorption sites generated by evacuation of FSM-16 at high temperature such as 1073 K react with propene under UV light irradiation to form surface intermediates. While, in the second step, the intermediates thus formed react with propene under the light including the visible region to form metathesis products.