A differential data transferring system and method uses three level voltages to simultaneously transfer three signals (for example, two data signals and one clock signal) across two transfer line sets (i.e., four transfer lines). Therefore, the differential data transferring method increases transferring efficiency by using fewer transfer lines. Also, according to the differential data transferring system and method, one of two transfer lines forming a transfer line set is controlled to a middle voltage level, while the other transfer line is controlled to either a high voltage or a low voltage. Accordingly, the voltage difference between the two transfer lines may be maintained at a constant amplitude. Additionally, the difference between first and second dividing voltages DC1 and DC2, which are used for generating a reference output data, is controlled to maintain a constant amplitude. Therefore, the differential data transferring system and method may provide improved operation reliability.