Objective To establish a HPLC method for determining Baicalin in Chaigejieji decoction. Method Baicalin was separated on ODS Kromasil C18 column with a mobile phase of methanol-water- phosphoric acid (47∶53∶0.2) and detected at 280 nm with a flow rate of 1.0 mL/min. Results The calibration curve was linear at the range of 0.3373～1.6865 ?g (r =0.9997). The average recovery of Baicalin was 97.87% and RSD was 1.66%. Conclusion It is a simple and accurate method for the determination of Baicalin in Chaigejieji decoction.