Twenty-two patients with myelodysplastic syndromes (MDS) were treated with thalidomide plus arsenic trioxide (ATO). Twenty-two MDS patients receiving supportive care were used as controls. The remission was achieved in 4 patients (18.2%) receiving thalidomide/ATO, and none in the control group (p<0.05). Fifteen of 22 patients in the treatment group achieved hematologic improvement (68.2% vs. 27.3% in the control, p<0.05). The progression-free survival was longer in the treatment group than that in the control (26 vs. 10 months, p<0.05). The overall survival was also longer in the treatment group than that in the control (36 vs. 16 months, p<0.05). No severe adverse reactions were observed. These preliminary findings suggest that thalidomide/ATO combination treatment is effective and safe for MDS.