Objective:To investigate the relation of blood arsenic concentration (BAC) with clinical effect and safety of arsenic-containing Qinghuang Powder(青黄散, QHP) in patients with myelodysplastic syndrome (MDS).Methods:Totally 163 patients with MDS were orally treated with QHP for 2 courses of treatment,3 months as 1 course.The BACs of patients were detected by atomic fluorescence spectrophotometry at 1,3,and 6 months during the treatment,and the effective rate,hematological improvement and safety in patients after treatment with QHP were analyzed.Results:After 2 courses of treatment,the total effective rate was 89.6％ (146/163),with 31.3％ (51/163) of hematological improvement and 58.3％ (95/163) of stable disease.The hemoglobin increased from 73.48 ± 19.30 g/L to 80.39 ± 26.56 g/L (P＜0.05),the absolute neutrophil count increased from 0.81 ± 0.48 × 109/L to 1.08 ± 0.62 x 109/L (P＜0.05),and no significant changes were observed in platelet counts (P＞0.05).Among 46 patients previously depended on blood transfusion,28.3％ (13/46) completely got rid of blood transfusion and 21.7％ (10/46) reduced the volume of blood transfusion by more than 50％ after treatment.The BACs were significantly increased in patients treated for 1 month with 32.17± 18.04 μg/L (P＜0.05),3 months with 33.56 ± 15.28 μ g/L (P＜0.05),and 6 months with 36.78 ± 11.92 μ g/L (P＜0.05),respectively,as compared with those before treatment (4.08± 2.11 μ g/L).There were no significant differences of BACs among the patients treated for 1,3 and 6 months (P＞0.05).The adverse reactions of digestive tract during the treatment were mild abdominal pain and diarrhea in 14 cases (8.6％),and no patients discontinued the treatment.The BACs of patients with gastrointestinal adverse reactions were significantly lower than those without gastrointestinal adverse reactions (22.39 ± 10.38 vs.37.89 ± 11.84,μ g/L,P＜0.05).The BACs of patients with clinical effect were significantly higher than those failed to treatment (40.41 ± 11.69 vs.23.84 ± 12.03,μ g/L,P＜0.05).Conclusion:QHP was effective and safe in the treatment of patients with MDS and the effect was associated with BACs of patients.