UNLABELLED: In this study, we prepared iron oxide nanoparticle and doxorubicin-loaded multifunctional nano-carrier (IONP/DOX-MFNC), capable of simultaneous cancer targeting via a herceptin monoclonal antibody, controlled anticancer drug delivery, as well as imaging modalities of magnetic resonance imaging (MRI) and near-infrared fluorescence (NIRF) imaging. IONP and DOX were efficiently loaded into the nano-carrier, and a desirable pH-responsive release of DOX was achieved by MFNC. The nano-carrier showed much higher cellular uptake and stronger cytotoxicity to HER2 overexpressed SK-BR-3 (human breast cancer cells) than MCF-7, a negative control cell, suggesting specific cancer targeting via HER2 receptor. In an in vivo tumor xenograft model, IONP/DOX-MFNC showed higher tumor uptake and significantly enhanced tumor regression than the nano-carrier without the antibody. Thus, DOX-loaded, multi-functional nano-carrier with HER2 antibody was effective for both imaging and therapy, showing the potential for early stage cancer diagnosis and simultaneous therapy. FROM THE CLINICAL EDITOR: In this study, efficacy -both for imaging and treatment - was demonstrated on a doxorubicin and iron oxide nanoparticle loaded multifunctional nano-carrier with HER2 antibody to show the potential for early stage cancer diagnosis and simultaneous therapy.