Abstract: Abstract:Objective To investigate the therapeutic efficacy of radioimmunotherapy of iodine-¹³¹ labeled Rituximab using intratumor injection（IT）in nude mice with xenografted raji cells tumor. Methods Iodine-¹³¹ labeled Rituximab was carried out by IODO-GEN method. The nude mice bearing raji cells tumor were divided into six groups based on the injected marked-drugs.The size of the tumor was measured every 2～3 day and the inhibition rates of different groups were calculated. Results The tumor inhibition rates of ¹³¹I-Rituximab IT group were higher than those of IP group, ¹³¹I-IgG IT group and cell control group（P<0.05）. ¹³¹I-Rituximab with intratumor injection in different dose showed that inhibition rate of low dose group was lower than that of high group, while there was no significant difference（P>0.05）. Conclusion Iodine-¹³¹ labeled Rituximab with intratumor injection showed the highest radioimmunotherapy efficacy which offered the experimental evidence for clinical application in the futrue.