Objective To explore a promising system for tumor CD 44 receptor-targeted imaging and to investigate their physic-chemical properties and targeting effect on CD 44 abundant cancer cells in vitro.Methods The superparamagnetic iron oxide ( SPIO) nanoparticles were prepared by a coprecipitation in alkaline media starting from a mixed of the ferrous and ferric solution.And then the surface of the SPIO nanoparticles were modified with APTMS by a reaction with the hydroxyl groups.Finally, the hyaluronan-modified SPIO ( SPIO-HA) nanoparticles were prepared.Control and experimental groups were established after adding SPIO or SPIO-HA as agents respectively.Transmission electron microscopy ( TEM) and particle size analyzer were used to measure these nanoparticle sizes and the hydrodynamic diameters.Thermogravimetric analysis ( TGA) was carried out to evaluate the HA-content on the surface of SPIO-HA.The MRI T2 ralaxivities (1/T2 ) of the two groups at different Fe concentrations (0.09, 0.18, 0.27, 0.36, 0.45 mmol/L ) were measured on a 3.0T MR system.HepG2 cells and HL7702 cells were used for assessment of cells viability by methyl thiazolyl tetrazolium ( MTT ) assay.Prussian blue staining , immunoassay fluorescence image and flow cytometry were carried out to determine the targeted cellular uptake of SPIO-HA nanoparticles.MRI were performed to show the MR T 2 value changes after incubating with HepG2 cancer cells by using T 2 WI sequences at a clinical 3.0 T MR system.One-way analysis of variance was performed to determine significant changes in MR T 2 values of blank control , SPIO-HA and SPIO groups.Results The SPIO-HA and SPIO NPs were fairly homogeneous with an average core size of 18.2 and 22.4 nm, hydrodynamic diameter of 91.1 and 103.2 nm, Zeta potential of (-45.00 ±0.86) mV and (-18.50 ±0.73) mV, and magnetic relaxivity of 0.212 ×106 M-1 · s-1 and 0.191 ×106 M-1 · s-1.Based on the TGA data , HA accounted for 24%weight of each SPIO-HA.The internalization of the SPIO-HA was confirmed by prussian blue staining , while the cells showed no obvious blue stains with SPIO , incubation of SPIO-HA with tumor cells led to blue color inside the cells.After that, we examined cancer cell binding of FITC-SPIO-HA by immunoassay fluorescence image and flow cytometry.The green fluorescence resulting from FITC-SPIO-HA was observed inside the cells in both the cytoplasm and the plasmalemma.Tumor cells treated with SPIO-HA exhibited higher fluorescence signals with 7.97-fold enhancement observed for HepG 2 cells over control particles.In vitro MR, mean T2 values of blank control , SPIO and SPIO-HA groups were ( 115.20 ±0.36 ), ( 115.07 ±0.81 ) and ( 21.67 ±0.21 ) ms, respectively.There was significant difference among those three groups (F=31 703.339,P<0.01), MR T2 values of HepG2 cells treated with the SPIO-HA NPs were lower than blank and SPIO group.In comparison, SPIO did not generate any MRI signal changes compared with blank group.Conclusion The tumor CD44 receptor-targeted MR molecular probe SPIO-HA had a good physic-chemical property and well targeted HepG2 cells.