In this work, we directly coated a layer of tannic acid (TA)-Mn2+ chelate networks on black phosphorus (BP) nanosheets (BPNSs) via a simple one-step method. The as-synthesized TA-Mn2+ chelate-coated BPNSs (BPNS@TA-Mn) have excellent T1 MRI contrast enhancement capability, good photoacoustic imaging performance, and high photothermal conversion efficiency, showing great potential in imaging-guided photothermal therapy.