Objective: To assess the therapeutic efficacy and toxicity of radionuclide therapy with Samarium-153-ethylenediaminetetramethylene phosphonic acid (153Sm-EDTMP) and the therapy with pamidronate disodium in the patients with painful metastatic bone cancer. Subjectts and Methods: Eighteen patients histopathologically confirmed malignancy with multifocal bone metastases were randomized into group A (9 patients treated with 153Sm-EDTMP) and group B (9 patients treated with pamidronate disodium) prior to study. The pain score in each patient prior to therapy was more than 6 according to a scoring technique for bone pain. Therapeutic response was classified in 4 grades (inefficient, mild response, effective and excellent relief). Results: In group A: 7 of 9 patients (77.8%) showed effective, 2 cases (22.2%) showed mild response. The therapeutic effective rate of 153Sm-EDTMP was 77.8%. Transient myelosuppression was generally mild and reversible with WBCs and platelets recovering after week 6. In group B: we found 4 cases inefficient, 1 case mild response, 3 cases effective and 1 case excellent relief, with the therapeutic effectiveness of 44.4%. No hematological toxicity was noted. Conclusion: The results from our study revealed that the therapeutic effectiveness of 153Sm-EDTMP was much higher than that of pamidronate disodium, for pain relief maintained more than 3 weeks, but its incidence of blood toxicity was more significant than that of pamidronate disodium.