Aim To study the influences of miR-203 on ursolic acid (UA ) sensitivity in leukemic K562 cell.Methods In the experimental system,eukaryot-ic expression vector of hsa-miR-203 (PmiR-203 )was transfected into K562 cells using LipofectamineTM 2000.K562 cells were incubated with different con-centration of UA alone or in combination with PmiR-203 .The cell proliferation was analyzed by MTT as-say.The cell apoptosis was measured by double stai-ning with Annexin V and Propidium Iodide.The ex-pression of Bcr/abl protein was detected by Western Blot.Results The miR-203 promoted the sensitivity of UA by up to 1 .55-fold and the IC50 was reduced from 44.3μmol · L-1 to 30.7 μmol · L-1 .The a-mount of apoptotic cells was increased in UA combined with PmiR-203 group (P<0.05).PmiR-203 downreg-ulated the expression of Bcr/abl protein in K562 cells. Conclusion Our results support a substantial role of miR-203 that enhances UA sensitivity in K562 cell and the mechanism appears to be related to the dounregula-tion of Bcr/abl by miR-203 .