During the long history of development of haemoglobin (Hb)-based O2 carriers (HBOCs), many side effects of Hb molecules have become apparent. They imply the physiological importance of the cellular structure of red blood cells. Hb-vesicles (HbV) are artificial O2 carriers that encapsulate concentrated Hb solution with a thin lipid membrane. We have overcome the intrinsic issues of the suspension of HbV as a molecular assembly, such as stability for storage and in blood circulation, blood compatibility and prompt degradation in the reticuloendothelial system. Animal tests clarified the efficacy of HbV as a transfusion alternative and the possibility for other clinical applications. The results of ongoing HbV research make us confident in advancing further development of HbV, with the expectation of its eventual realization.