We conducted a phase II trial to investigate the safety and efficacy of alemtuzumab in treating steroid-refractory acute graft-versus-host disease (aGVHD) grade II or higher after stem cell transplantation. Ten adult patients (6 with aGVHD grade III and 4 with aGVHD grade IV) were included in the study. Nine patients had gastrointestinal tract involvement, 7 had skin involvement, and 5 had liver involvement. Five patients responded to treatment, 2 with complete response and 3 with partial response. Eight infectious events (4 of grade 3-4) and 7 cytomegalovirus (CMV) reactivations were observed. Six patients had grade 3-4 cytopenia. All 10 patients died (7 resulting from aGVHD progression, 2 from severe infection, and 1 from to leukemia relapse), at a median of 40 days (range, 4 to 88 days) after alemtuzumab treatment. Overall, our findings suggest that steroid-refractory aGVHD may be improved by treatment with alemtuzumab, but that this treatment does not overcome the dismal prognosis of patients with severe aGVHD, demonstrating the need for alternative therapies to treat this complication.