Aim: The usefulness and safety of strontium chloride (89Sr), a radiopharmaceutical agent for painful bone metastasis, varies from patient to patient, but the reasons for why the usefulness and safety vary have not been elucidated. The purpose of this study is to explore the background factors of patients who experienced pain relief or bone-marrow suppression after 89Sr was administrated. Methods: In the cases of pain relief, we divided the results from a numeric rating scale (NRS) before and after 89Sr administration into effective and ineffective groups as outcomes. In the cases of bone-marrow suppression, we analyzed neutrophil cells, blood platelets, and hemoglobin levels, respectively, before and after 89Sr administration as outcomes. Then, we performed statistical analyses on both case groups. Results: The results showed that the background factors associated with pain relief were weight, the 89Sr dosage amount, NRS, eGFR, SCr, and Ca levels before 89Sr administration and the area of bone metastasis (number of sites reached). We found that background factors associated with bone-marrow suppression have a moderate significant correlation with hemoglobin, NRS, and SCr levels before 89Sr administration after investigating factors which influence neutropenia. In the case of thrombocytopenia, there was a moderate significant correlation with platelet counts before 89Sr administration. In the case of hypochromia, there was a moderate significant correlation with hemoglobin levels before 89Sr administration. Discussion: Our study could elucidate patient background factors associated with pain relief and bone-marrow suppression after 89Sr administration.