In this work, the authors presented a sensitive and accurate optical method for measuring the variation of the refractive index of sugar solution (sucrose) with various concentrations (10%-50%). The method is based on finding a critical angle of a laser beam impinging on a microchamber filled with a sugar solution. The chamber is attached to a semicircle glass block and mounted on a stage attached to a stepping motor (geared at 100:1 ratio) for finely adjusting the incident angles. The intensity of the reflected laser light is monitored by a linear sensor array. The stepping motor control and the signal read from the sensor array are done with an Arduino microcontroller. Once the critical angle is obtained, the refractive index is calculated from Snell’s law at the critical angle. This method has many advantages such as being highly sensitive, having high stability and repeatability, and requiring only microliters of liquid sample, inexpensive optical, and electrical components. Our method showed that the refractive indices of sucrose solutions vary linearly with the sugar concentration of sugar in the range of 0 to 50% and the precision of the measurement is estimated to be better than 0.10% (the standard deviations are in the range of 0.04-0.10%), which is well below the limit set by the Association of Official Agricultural Chemists (AOAC). It suggests that, with a little further development to improve user-friendliness, our method could be used with confidence to quantify sugar concentrations in real liquid samples, such as soft drinks beverages, and juices where sugar contents are often listed as a whole percentage or even in whole blood.