Superparamagnetic iron oxides can be used as contrast agents for MR T2-weighted imaging. We created multifunctional nanoparticles based on Fe3O4, Trastuzumab and indocyanine green (ICG) to target HER2 positive breast cancer cells in vitro and vivo. Firstly, internalization was assessed on HER-2 positive breast cancer SK-BR-3 cells by transmission electron microscopy (TEM). Furthermore magnetic resonance imaging (MRI) and fluorescence imaging were used to examine the biodistribution and its targeting effect in vivo. Additionally, photothermal therapy (PTT) was further evaluated to examine the treatment effect of NPs. As a result, Fe3O4-trastuzumab-ICG have shown great potential to become an effective multifunctional imaging agent and a tool for photothermal therapy for HER-positive breast cancer.