We describe a sensitive polarimeter for measuring optical rotation induced by chiral molecules in solution that operates in the reflectance mode. A polarized light beam is made to pass through a liquid sample two or more times before detection by reflecting the beam from the surface of the sample container. The optical activity of the sample is measured using a differential polarization detector. Our results show that, for certain initial polarization states and angular orientations of the beam with respect to the glass interfaces, high sensitivity to changes in the concentration of the sample can be achieved. Results of a theoretical analysis of the technique were confirmed by experiments in which optical rotation of glucose in water was measured using a simple apparatus that employs a light‐emitting diode source. Glucose sensinginvivoand on‐line monitoring of industrial processes using integrated optoelectronic sensors are discussed as potential applications.