ErbB2, which belongs to the epidermal growth factor receptor (EGFR) family, plays a key role in human malignancies. ErbB2 is overexpressed in approximately 30% of human breast cancers and in many other cancer types, including stomach, bladder, ovarian and lung carcinomas. The objective of this study is the development of anti-ErbB2 aptamer-modified T2 contrast agent based on magnetic nanoprobe (AptErbB2-MNP) having high-specificity onto Erbb2-expressing cancer. For confirmation of AptErbB2-MNP as T2 contrast agent, T2 relaxivity and hydrodynamic diameter was measured. in vitro binding affinity tests were conducted not only recombinant ErbB2 proteins but also the live cells. in vivo targeting ability was verified by in vivo MRI analysis.