Several methods of taste evaluation, such as sensory tests and the use of electronic tongues and a taste-sensing system based on lipid/polymer membranes, have been developed and utilized in the food and pharmaceutical fields. In particular, the taste-sensing system can individually quantify five basic tastes using each type of sensor membrane. However, it is difficult to develop a sweetness sensor, because sweeteners cover a large number of compounds with diverse chemical structures and sizes. Using membrane potential measurements, the taste-sensing system needs three types of sensor membrane for each electric charge type (neutral, negative and positive) of sweetener. The sweetness sensor for uncharged sweeteners has been commercialized, but the mechanism of the response to sugars has not been clarified. Therefore, we investigated how the sensor responds to sugars in this study. As a result, we confirmed the unnecessity of the aromatic ring and that of the carboxyl group and the basic sensor-rinsing solution including cations, and concluded that both the hydrophobicity and electric charge of the surface of the sensor membrane influence the sweetness response.