Abstract: In order to improve the detection sensitivity of optical activity,based on Zeeman effect,a common-path heterodyne interferometer was developed to measure the optical activity of liquid.In this heterodyne interferometer,a pair of correlated orthogonal linear polarized beam is emitted from a Zeeman He-Ne laser,which reduces the complexity of the optical system greatly.A balanced detector and a differential amplifier are integrated into this interferometer so as to reduce the excess noise induced by laser intensity fluctuation and external environments significantly.Thus,a shot-noise-limited detection of this interferometer can be achieved.The optical activity of glucose solution with concentration of(0~50)mg/dL was measured with this common-path heterodyne interferometer and the detection sensitivity was up to 2.3×10-5 degree.This simple heterodyne interferometer can be applied in the optical activity analysis of solid-state,liquid-state or gas-liquid material.