Abstract: A description is given for the preparation of flow through sensor and of the incorporation of the sensor into a flow injection analysis system. The parameters affecting the measurement are discussed. An accurate, convenient and rapid method is proposed for the determination of berberine- type alkaloids in various Chinese patent medicines (Coptis chinensis Franch.,Phellodendron chinensis Schneid., Xianglian Wan,Zuojin Wan, Ermiao Wan and Sanmiao Wan). The slope is 54 ～ 60 mV/decade over the concentration range of 10-3～3×10^-6 mol/L berberine at pH 2～9.5. Direct potentiometry determination of berberine in various samples showed an average recovery of 99.5 ～103.5% and a relative standard deviation of 1.3～ 3.5% at a sampling rate of 120/h.