Unrelated donor (URD) is an acceptable source of stem cell grafts for adults. With the growth in available URD, improved human leukocyte antigen (HLA) typing technology and better understanding of HLA matching, the number of URD haematopoietic stem cell transplantation (URD-HSCT) is increasing dramatically in recent years. Peripheral blood stem cells have surpassed bone marrow as the preferred stem cell source for URD-HSCT, and more unrelated cord blood transplantations have been successfully performed in adults. Majority of URD transplants are for haematological malignancies, and acute leukaemia has become the most common disease, while the percentage of older patients receiving URD transplants is increasing. Clinical advances in URD-HSCT have greatly improved the outcomes, which are now comparable to related donor HSCT, however, transplant-related mortality (TRM) remains the most considerable problem in URD-HSCT. It is worth noting that non-myeloablative or reduced-intensity conditioning regimens have been introduced and utilised increasingly in URD-HSCT recently, which reduce the TRM and expand eligible patients for URD-HSCT. Since the family size is decreasing in China, URD represents the most common alternative source of stem cell for HSCT. However, further improvements are necessary in the setting of URD-HSCT.