Patients after allogeneic hematopoietic SCT (HSCT) are at risk of malnutrition. To assess the impact of malnutrition after allogeneic HSCT on transplant outcomes, we conducted a retrospective study. Adult patients who received allogeneic HSCT from 2000 to 2009 for standard-risk leukemia and achieved disease-free survival up to 3 months after allogeneic HSCT were included. From participating centers, 145 patients were enrolled. Median age was 46 years (19-68). Patients were classified based on weight loss during 3 months after allogeneic HSCT as follows: normal group (weight loss <5%, n=53), mild malnutrition group (5%⩽weight loss<10%, n=47), severe malnutrition group (10% ⩽weight loss, n=45). The cumulative incidences of 2-year nonrelapse mortality (NRM) were 3.8% in the normal group, 8.5% in the mild malnutrition group and 27.3% in the severe malnutrition group. The probabilities of a 2-year OS were 73.2% in the normal group, 74.5% in the mild malnutrition group and 55.3% in the severe malnutrition group. In multivariate analysis, severe malnutrition was associated with an increased risk of NRM and a worse OS. In conclusion, weight loss ⩾10% was associated with a worse clinical outcome. Prospective studies that identify patients at risk of malnutrition and intervention by a nutritional support team are warranted.