Objective: To investigate the reversal effects of pulsed magnetic fields(PMF) on the drug resistant cell line K562/ADR in vitro and their mechanism.Methods: MTT assay was used to determine the IC50 of ADR on K562/S and K562/ ADR cell lines,the detriment of PMF on the K562/ADR cell line and the reversal effects of the drug resistance after treatment with different frequencies of PMF.Flow cytometry(FCM) was applied to the assessment of concentration of intracellular ADR.Results: The drug-resistance multiple of the K562/ADR cell line was 29.36.PMF did not affect the growth of the K562/ADR cell line.Different frequencies of PMF produced different effects on the IC50 of the K562/ADR cell line.In the same condition,70Hz PMF produced the most significant effect and increasea the concentration of intracellular ADR.Conclusion: PMF can reverse the multidrug resistance of K562/ADR by enhancing the drug concentration in K562/ADR cells,and its frequency is correlated with its reversal effect:low fregucncy produces better effect.