A system for measuring the rotation angle of optical active substances has a light source, a polarization generation unit; a polarization analyzing unit; a signal generating unit, respectively and electrically coupled to the polarization generation unit and the polarization analyzing unit; a signal processing unit, electrically coupled to the electric signal generating unit; wherein the light source is enabled to emit a beam toward the polarization generation unit for enabling the beam to be polarized into an incident polarized beam while being projected and traveled in an optical path passing through an optical active substance so as to be converted into a emerging beam; and the polarization analyzing unit is positioned to receive and analyze the emerging beam so as to generate a signal to be received and processed by the signal processing unit.