Magnetic resonance imaging (MRI) is widely applied in medical research and diagnosis, and a MRI contrast medium plays a crucial role in improving the sensitivity of detection. Ultrasmall superparamagnetic iron oxides (USPIOs) exhibit the potential as a enhancement contrast medium for MRI due to their excellent magnetic response performance; however, to endow them with specific tumor targetability, long-term circulation performance has always been a hot topic in this field. In this study, a well-designed procedure of chemical coprecipitation, surface modification, and peptide grafting was applied to prepare the active tumor-targeting USPIOs@F127-WSG, in which Pluronic F127 (F127) and the peptide WSGPGVWGASVK (peptide-WSG) were selected as the template agent and the ovarian tumor-targeting ligand, respectively. The results showed that single USPIOs@F127-WSG particles were FeO nanoparticles regulated by the confinement effect of F127 micelles with a uniform globular morphology and size (∼9 nm), and peptide-WSG was grafted for their tumor targetability. USPIOs@F127-WSG particles presented superparamagnetic behavior with high relaxivity ( = 278.15 mM s) and in vitro targetability for SKOV-3 cells due to the special binding between peptide-WSG and specific receptors of SKOV-3. The test results in vivo verified the targetability of USPIOs@F127-WSG by their specific aggregation in the tumor regions, leading to the -weighted MRI contrast enhancement. These outstanding properties indicate that USPIOs@F127-WSG have great potential to be applied as the active tumor-targeting contrast agent for MRI.