Molecular magnetic resonance imaging (mMRI) has been paid more and more attention for early diagnosis of cancer. A sensitive and specific mMRI probe plays the most important role in this technique. In this study, superparamagnetic iron oxide (SPIO) nanoparticles and mAb G250 were conjugated as mMRI probe for the detection of clear cell renal cell carcinoma (ccRCC) using 3.0-Tesla MRI in vitro. mAb G250 could specifically recognize carbonic anhydrase IX (CAIX) antigen overexpressed in ccRCC and the SPIO nanoparticles as MRI contrast agent presented excellent MRI response and good biocompatibility. The successful assembly of this nanoprobe was confirmed by UV-vis spectrum, FT-IR spectroscopy and DLS analysis. In vitro MRI study on ccRCC cells and control cells indicated that our fabricated mAb G250-SPIO nanoprobe could be used in the specific labeling of clear cell renal carcinoma cells successfully.