Amino-dextran-functionalized superparamagnetic iron oxide nanoparticles (SPION) were synthesized by two-steps: Dextran-modified SPION was obtained by one-step co-precipitation method. Then, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) was added to the resultant dextran-SPION to prepare amino-dextran-functionalized SPION (AEAPS/Dex-SPION). The particles were characterized by vibrating sample magnetometer (VSM), transmission electron micrographs (TEM), atomic force micrographs (AFM), gas chromatography and atomic absorption spectrophotometry. The size of the modified particles varied in a range of 30 to 40nm and did not change significantly after modification. The binding rate of AEAPS was 91.15%. A monoclonal antibody against S100 (anti-S-100), a gold standard for the diagnosis of melanocytic lesions, was conjugated to the AEAPS/Dex-SPION to prepare immuno-SPION. From the result in melanoma B16 cell, the immuno-SPION was proven to have a bio-targeting activity. Such AEAPS/Dex-SPION might be very useful for bio-magnetically targeted detection in early melanocytic lesions.