Abstract: The radioiodinated 7α-O-iodoallyl diprenorphine (7α-O-IA-DPN) as a new opioid receptor imaging agent for SPECT study is developed. The design and radiochemical synthesis of 7α-O-IA-DPN labeled with iodine-125 are performed. In vitro and in vivo opioid receptor binding assays, and in vitro stability are studied, respectively. The radiochemical purity of radioiodinated 7α-O-IA-DPN is more than 95%, and still greater than 90% kept for 24 h at room temperature. Radiochemical yields is 81%～90%, and specific radioactivity is 83.25 PBq/mol. The binding assay in vitro shows a very high affinity(K_d=0.23 nmol/L) with B_(max) of 38 pmol/g. The proposed compound of 7α-O-IA-DPN appears to be a potential opioid receptor imaging agent for SPECT study.