We propose new instrumentation to measure the refractive index (RI) of transparent liquids as a function of temperature. The physical phenomenon used to carry out the measurement is the light refraction that occurs in transparent liquids. A width change in a reference object is produced by light refraction, which is related to the RI. Image processing was used to measure the object width using an image from a digital microscope. The instrument measures the RI from a range of 15°C to 100°C with an accuracy of 10^−  4  %  . The measurement procedure was calibrated with distilled water and acetonitrile samples, and the Sellmeier and Cauchy equation was used to compare our results. Finally, as an appropriate application, the RI of lophine in a solution was measured.