Disclosed are a nanoparticle sensor for measuring protease activity, for protease imaging, and a method for preparing the same. More specifically, the present invention relates to a nanoparticle sensor for measuring protease activity in which a fluorophore- and a quencher-conjugated peptide substrate is conjugated to a biocompatible polymer nanoparticle. The peptide substrate is specifically lysed by a protease. The sensor according to the present invention is capable of inhibiting emission of fluorescence with high extinctive activity of the quencher on a fluorescent material. But strong fluorescence is specifically emitted only if the peptide substrate is lysed by a specific protease. Therefore, the sensor is especially useful as a method for screening a novel drug such as a protease overexpression inhibitor, and early diagnosis of incurable diseases and various diseases such as autoimmune diseases including cancer, osteoarthritis, rheumatoid arthritis and dementia.