The refraction index (RI) of liquids provides valuable information about their physical properties, e.g. concentration and density. Knowing RI of a liquid it is possible to determine and control its composition, which is topical for funda¬mental research, chemical analyses, medical diagnostics, etc., as well as in diversi¬fied material processing technologies. We have created a highly sensitive compact and adaptable device for RI measurements, which is suitable for analysis and real¬time technological control of stationary and flowing liquids (aggressive included). The operation of the proposed measuring device is based on the determination of a laser beam deviation when it is passing through a cylindrical cuvette with the liquid to be analysed. This deviation depends on the liquid's RI, which is determined by projecting the outcoming laser beam onto a linear sensing measuring element, e.g. linear CMOS or CCD image sensor. To significantly raise the measurement sensitivity at RI determination and provide the compactness of the design, an effective solution has been worked out, which is based on the repeated refraction and reflection of the beam when it passes through a cuvette filled with the liquid under test; this augments the changes of the beam's centric angle many times depending on the RI. One more proposal for increasing the measurement resolution and image contrast resolution is a partial coverage of the cuvette with a reflecting layer, which allows increase in the outcoming laser beam light intensity. A new method of image analysis is also proposed for detection of the laser beam position using a linear sensor in which the beam's projection image is created. The method ensures higher measurement stability and accuracy. The new concept of attaining higher sensitivity and stability of laser-based optical RI measurements using a cylidrical cuvette provides possibility to set up a compact precise optical measuring system.