Novel core-shell hollow mesoporous Prussian blue @ Mn-containing Prussian blue analogue (HMPB@MnPBA) nanoparticles, designated as HMPB-Mn, as an intelligent theranostic nanoagent, are successfully constructed by coating a similarly crystal-structured MnPBA onto HMPB. This can be used as a pH-responsive T-1-weighted magnetic resonance imaging contrast agent with ultrahigh longitudinal relaxivity (r(1) = 7.43 m M-1 s(-1)), and achieves the real-time monitoring of drug release.