The objective of study was to investigate the effect of low-dose antithymocyte globulin (ATG) on steroid-resistant severe acute graft versus host disease (aGVHD). Six patients with steroid-resistant severe aGVHD after haploidentical bone marrow transplantation (BMT) received the treatment with ATG at a low dose of 1.25 mg/kg for 3 - 5 doses every other day. The results showed that 3 out of 6 patients got completely remission (CR), among them 2 patients have still been in disease-free survival, 1 patient died from leukemia relapse. 1 out of the other 3 patients got partial remissin (PR), 2 patients were aggravated. The other 3 patients all died from GVHD. The major complications observed in these patients were infections. In conclusion, low-dose ATG is effective for some patients with steroid-resistant severe aGVHD, and has not severe side effect. To strengthen environmental protection should be considered as important for prevention of infection.