Abstract： @@ Tongue lesions resulting from mucositis are a frequent complication of high-dose chemotherapy and irradiation. They are very common in patients with hematopoietic stem cell transplantation, and tongue lesions due to other causes have also been reported. Black hairy tongue (BHT) is a special tongue lesion, not rare in the population with tobacco abuse, but so far it has not been reported after allo peripheral blood hematopoietic stem cell transplantation (allo-PBHST). Here we presented a patient who developed BHT after allo-PBHST and discussed the factors that may cause this condition.