Transition-metal ion copper(II) (Cu(II)) has drawn increasing attention as a small-molecular cancer theranostic agent. However, delivering a sufficient dosage of Cu(II) to the tumor site and integrating multiple imaging modalities to achieve precise and effective cancer theranostics remains a critical challenge. Herein, an emerging Cu(II)-based nanocomposite has been synthesized for targeted tumor computed tomography (CT)/magnetic resonance (MR) dual-mode imaging and chemodynamic therapy (CDT). Briefly, 2-picolinic acid (PA-COOH), polyethylene glycol (PEG)-linked folic acid (FA), and fluorescein isothiocyanate (FI) were sequentially conjugated with polyethylenimine (PEI.NH