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Objective The separation of tumor diagnosis and treatment is one of major issues in the clinic.Use of activatable theranostics for the combination of diagnosis and treatment of cancer can provide the direct evidence to early diagnosis ,occurrence and development progresses of cancer, and also enables online imaging of drug for the detection of cancer,image-guided drug delivery and treatments,guidance of surgical resection,and monitoring of treatment response.Herein,we report a radionuclide 64Cu labeled magnetic melanin nanopaticles (64Cu-MMNs) for positron emission tomography (PET), magnetic resonance imaging (MRI), and photoacoustic (PA) tri-modal imaging guided photothermal therapy (PTT) of U87MG glioblastoma cancer.Methods MMNs were synthesized by biomimetic synthesis method using bioploymer melanin as the biotemplate.The radionuclide 64Cu was labeled with MMNs by the high affinity of metal ions of melanin.PET, MRI, and PA imaging were carried out on U87MG tumor-bearing mice.PTT was conducted both in vitro and in vivo.Results and Discussions MMNs were successfully synthesized by biomimetic synthesis method.The size of MMNs is ~15 nm.The r2 value of MMNs is 167.28 mm-1 ·s-1 ,which is much higher than spherical magnetic nanoparticles [10 nm, r2=(59.91±6)mm-1· s-1 and 16 nm, r2=(125.86±9)mm-1· s-1].MMNs were successfully radiolabeled with 64Cu and purified to give radiochemical yield ~100%.64Cu-MMNs were stable in PBS and mouse serum up to 24 h.In vivo PET imaging showed high tumor uptake of MMNs after intravenous injection (150 μCi, ~10% ID/g, 24 h).MRI and PA imaging also showed high tumor uptake of MMNPs.Afterwards, upon localized laser irradiation(808 nm, 0.5 W/cm2, 5 min), 100% tumor elimination was achieved in MMNP treatment group(10 mg/kg of MMNs).Conclusion MMNs showed great potential as cancer photoactivatable theranostics with PET/MRI/PA multi-modality imaging capability and potent PTT effect.