We present a method to characterize optical properties of liquids by spectroscopic ellipsometry. The experiments use a specific liquid cell that avoids disturbance of waves at air-liquid interface and allows the determination of the real and the imaginary part of the refractive index, with a sensitivity of the latter below 10(-4). The method is illustrated by results obtained with a spectroscopic phase modulation ellipsometer on several liquids such as deionised water, microscope oil and protein solution. Comparisons of the method with standard techniques are given. (C) 2016 Elsevier B.V. All rights reserved.