Objectives: Fatigue is a common symptom in allogeneic-hematopoietic stem cell transplantation (allogeneic-HSCT) recipients. However, effects of severe fatigue on pulmonary functions, blood cells, dyspnea, muscle strength, exercise capacity, depression and quality of life (QOL) in allogeneic-HSCT recipients are still unknown. Therefore, to compare pulmonary functions, blood levels, dyspnea, muscle strength, exercise capacity, depression, and QOL between allogeneic-HSCT recipients according to fatigue severity and to determine predictors of severe fatigue were aimed in the current study. Methods: Twenty-four severe-fatigued (Fatigue Severity Scale score >= 36) (40.08 +/- 12.44years) and 25 non-severe-fatigued (36.20 +/- 13.73years) allogeneic-HSCT recipients were compared. Blood levels, pulmonary functions (spirometer), dyspnea (Modified Medical Research Council Dyspnea scale), exercise capacity (6-minute walk test), depression (Beck Depression Inventory-II), QOL (European Organization for Research and Treatment of Cancer QOL Questionnaire), respiratory (mouth pressure device) and peripheral muscle strength (dynamometer) were evaluated. Results: Symptom QOL-subscale and depression scores were significantly higher; peripheral muscle strength, global health status, and functional QOL-subscales scores were lower in severe-fatigued recipients (p < 0.05) whose exercise capacity was clinically (28.85 m) decreased. Blood levels, pulmonary functions, dyspnea, and respiratory muscle strength were similar in groups (p > 0.05). 42.4% of the variance in severe fatigue was explained by symptom QOL-subscale score and corticosteroid use after HSCT (p < 0.001). Conclusions: Impairments in peripheral muscle strength, QOL, exercise capacity, and depression are more prevalent among severe-fatigued recipients. Moreover, poorer QOL and corticosteroid use after HSCT are most important predictors of severe fatigue. Effects of comprehensive exercise programs and psychosocial support for severe-fatigued recipients in late post-engraftment period should be investigated.