By reducing non-specific macrophage uptake, anti-biofouling polymer coated iron oxide nanoparticles (IONPs) conjugated with mannose as the ligand (Man-IONP) was developed for specifically targeting sub-type tumor associated macrophage M2 with mannose receptor 1 expression. This novel MRI probe demonstrated specific M2 macrophage targeting in vitro with M1 and R264.7 macrophages as controls. Immuno-staining of 4T1 breast tumor tissues with Man-IONPs showed the probe targeting M2 similarly to anti-CD206 antibody. NIR and MR imaging of 4T1 tumor-bearing mice showed significant contrast changes after receiving i.v. injection of NIR dye labeled Man-IONP, while little change was observed for mice receiving non-targeted IONP.