Abstract: The biodistribution and SPECT imaging of ¹²³I labeled 3H11(¹²³I-3H11) monclonal antibody in tumor-bearing mice were investigated. The biodistribution results show the uptake rate in the tumor at 24h post-injection with （11.06±1.86）%ID/g. The uptake ratios of tumor to blood, tumor to thyroid, and tumor to stomach are 2.90±0.06, 1.51±0.42, and 9.96±0.56, respectively. SPECT imaging was performed at 2h and 24h post-injection of 7.4MBq ¹²³I-3H11. Clear imaging of tumor is obtained at 24h post-injection. The biodistribution results of labeled antibodies and their imaging rseults are basically identical.The results of biodistribution and SPECT imaging in tumor-bearing mice indicate that ¹²³I-3H11 may be a new promising SPECT tracer for imaging gastric cancer.