Abstract: OBJECTIVE To synthesis chitosan-coated ultrasmall superpara-magnetic iron oxide (USPIO) nanoparticles and cross-link with atherosclerosis-target-aptamer. METHODS First, Fourier transform infrared spectroscopy (FT-IR) was used to identify the composition of nanoparticles. Aptamer was cross-linked with particles and polyacrylamide gel electrophoresis (PAGE) was used to identify the connection rate. Later on, the obtained nanoparticles were characterized by X-ray powder diffraction(XRD), transmission electron microscopy(TEM), vibrating sample magnetometer(VSM, MPMS XL-7 system). RESULTS The USPIO were successfully synthesized and could be connect with aptamer in a high degree. The diameter of USPIO ranged from 10 to 20 nm. T₂ relaxivity was 0.284 2×10⁶ mol^-1·s^-1 and saturation magnetization was 108 emu·g^-1 Fe. CONCLUSION The USPIO linked with aptamer as an atherosclerosis targeting chitosan nanocarrier is successful, the natures fit the requirements for iron contrast agent in MRI.