Objective: We recently showed that co-transplantation of bone marrowderived spheroids (BM-spheroid) formed using 3D culture from BM-derived mononuclear cells (BM-MNCs) improve islet function and revascularization using a marginal mass renal subcapsular islet transplantation model. In the present study, we have expanded our previous studies to investigate whether co-transplantation of islets with BM-spheroid can also improve intraportal islet transplantation outcome. Methods: Using green fluorescent protein transgenic (GFP-Tg) mice, transplanted BM-spheroids were traced and the morphology of transplanted islets was assessed. The revascularization of intraportally transplanted islets was examined by immunohistochemistry. The efficacy of transplanted islets was investigated using a syngeneic marginal mass intraportal islet transplantation model. Blood glucose concentration was monitored for 1 month. Results: BM-spheroid co-transplantation with islets improved the post-transplant outcomes in terms of glucose tolerance, serum insulin levels, and diabetes reversal rate when compared with transplantation of islet alone. The area of individual islets within the graft-bearing liver was significantly higher in BM-spheroid co-transplantation compared to transplantation of islets alone. Fragmented islets were found more frequently within the graft-bearing liver in the islet alone transplantation group compared to the BM-spheroid co-transplantation group. Conclusion: Our results suggest that co-transplantation of BM-spheroids indicates a promising strategy for improving the efficiency of intraportal islet transplantation.