An efficient method was developed for the separation and purification of monacolin K acid from the crude extract of red yeast rice by pH-zone-refining counter-current chromatography(pH-ZRCCC).Monacolin K was first extracted from red yeast rice by 95%ethanol,then it was transformed from lactone to acid form by alkalization method and separated by pH-ZRCCC with the two-phase solvent system composed of petroleum ether/ethyl acetate/ methanol/water(5:5:4:6,V/V),10 mmol/L HCl in organic phase used as the stationary phase and 10 mmol/L NH_3 ? H₂O in aqueous phase used as the stationary phase.The purity of monacolin K acid form from separation fraction was analyzed by HPLC and identified by UV,ESI-MS and ~1H-NMR.From 2.0 g of crude extract,147 mg of monacolin K acid form was obtained at 93.4%purity in one-step separation.