An on-line refractometer made of easily obtainable materials is built to determine the concentration of an alcohol solution, and its performance is examined by applying to the system of ethanol and water. Since the refractive index and the temperature are measured simultaneously, it is possible to compensate the effect of temperature which is not available with an existing on-line refeactometer. Therefore, it can be implemented in the application of process control. The experimental outcome indicates that the home-made refractometer has satisfactory reproducibility and reasonable accuracy for the industrial application.