Chemotherapy is still a kind of important strategy for cancer treatment,but lacking effective delivery system limits the therapeutic outcome.Owing to the excellent biocompatibility,albumin has been employed as drug vehicle;however,it has to face complicated synthesis procedures and still needs an effective technology for the drug delivery evaluation.In this study,a facile method was utilized to prepare a protein-based theranostic system through the self-assembly of albumins with small molecules and drugs;furthermore,the paramagnetic divalent manganese ions were conjugated on the surface of the nanocomposite through a coordination bond and carried out the magnetic resonance imaging.This nanosystem with a stable structure exhibited about 80 nanometer size and 7.7[Mn]mM-1S-1 T1 relaxivity;moreover,the pH-sensitive drug releasing property and the imaging function empower it with theranostic cancer therapy.Moreover,the nanocomposites effectively entered into the cancer cells and showed superior antitumor ability;and these treated cells exhibited significant T1 signal.These results suggested that the albumin-based nanosystem is a novel chemotherapy drug delivery vehicle and a promising candidate for magnetic resonance imaging.