The present invention relates to a nanoporous thin film and a method for fabricating the same. The nanoporous thin film fabricating method for fabricating a nanoporous thin film with a composite photocatalyst structure for a photodegradation and a water purification includes providing a porous substrate with a plurality of through-nanopores therein, each of which through-nanopores have an inner tube wall; forming an oxide-based photocatalyst layer over the porous substrate and the inner tube wall by using a first chemical-based deposition process; and forming a metal-based photocatalyst layer on a part of the oxide-based photocatalyst layer by using a second chemical-based deposition process.