The present invention relates to a pH-responsive metal-catechol derivative nanoparticle for drug delivery based on a mussel adhesive protein, particularly Fe(III)-DOPA nanoparticle, and a method for preparing the same. A nanoparticle for drug delivery according to the present invention is prepared using a pH responsive substance, catechol derivative-metal complex, particularly Fe(III)-DOPA complex, based on a mussel adhesive protein. Thereby, the present invention has excellent biocompatibility, is capable of easily and quickly penetrating into a target cell, and releases a loaded drug under acidic conditions, which enables to selectively deliver a drug to a specific disease having an acidic environment.