OBJECTIVE: To explore the relationship between the efficacy of realgar for the treatment of myelodysplastic syndromes with multilineage dysplasia(MDS-MLD) and arsenic concentration in the peripheral blood of patients.METHODS: In this prospective study, a total of 50 MDS-MLD patients were treated with traditional Chinese drugs containing realgar for 3 months in Xiyuan Hospital from March 2018 to January 2019.Routine blood examination as well as liver and kidney function were monitored before and after treatment. The concentration of arsenic in the peripheral blood was measured using an atomic fluorescence spectrometer after treatment. The correlation between clinical effect and arsenic concentration was analyzed by Spearman's method.RESULTS: The treatment response rate was 54%.Two patients(4%) achieved complete remission,50%(25 of 50) showed hematologic improvement,and 23 patients had stable disease(23%). No disease progression was observed. Arsenic concentration in the peripheral blood ranged from 14.60 to85.96 μg/L. Clinical efficacy was positively correlated with arsenic concentration(P < 0.05). The incidence of mild adverse reactions was 16%.CONCLUSION: A relatively high concentration of arsenic in the peripheral blood may improve the clinical efficacy of realgar in MDS-MLD patients.