A new and accurate method has been developed by which all the components of the anisotropy of the optical susceptibilities can be determined. The apparatus based on this method has been constructed, and named as HAUP (High-Accuracy Universal Polarimeter). The basic principle is to measure the intensity of the light beam, which is propagated successively through a polarizer, a specimen, and an analyser, as functions of azimuth and deflecting angle from the crossed-Nicols condition. Thus the method is characterized by its extreme simplicity, which prevents systematic errors. Considerations and tests of inevitable systematic errors are made. The systematic errors originating in the parasitic ellipticities of the polarizer and analyser are found to be serious for the measurements of optical activity; appropriate solutions to remove them are devised here. Sensitivities of measurements of optical activity and birefringence by the HAUP method reach 4.8 × 10−8 and 2.2 × 10−6 respectively, the accuracy being 4.2 × 10−3 and 2.2 × 10−3 respectively. By using HAUP it has become possible to measure simultaneously all the components of optical activity, birefringence and rotation of optical indicatrix of any crystals, including those belonging to the monoclinic and triclinic systems. These measurements can be made from about 400 K down to 10 K. Also, simultaneous determinations of electrogyration and electrooptic coefficients have become feasible by applying electric fields to crystals.