Abstract: Objective 　To exploit the radioimmunoimaging of iodine-131 labeled anti-CD20McAb with intratumor injection( IT) in nude mice xenografted with raji cells tumor. Methods 　Iodine-131 labeled anti-CD20McAb by iodogen method. The mice were imaged by SPECT and killed following on one、three、seven and fifteen day after injection. The injected dose/ gramtissue ( %ID/ g) percentages of different organs, including tumor, blood, etal were measured by calibrator and calculated. Dosimetry of cumulate absorption in tumor was performed using MIRD formula. Results 　¹³¹I-anti-CD20McAb IT group showed clearer images in tumors than int raperitoneal injection ( IP) and ¹³¹I-IgGIT control groups. The %ID/ g in tumor in ¹³¹I-anti-CD20McAb IT group were 1. 4～17 fold higher than that in IP group and 1. 7～3. 7 in IgG IT group, and the cumulate absorbed dose were 6. 0～12. 6 and 1. 5～2. 5 fold higher than the other two groups. Conclusion 　Tumor could have the highest absorbed radioactive drugs with intratumor injection of ¹³¹I-anti-CD20McAb, which offered the experimental evidence for the next radioimmunotherapy.