A circuit for canceling a direct current (DC) offset in a communication system includes a digital-to-analog (D/A) converter assembly (30), a summing circuit (40), an inphase-to-quadrature (I/Q) modulator (50), a detecting module (70), and a microcontroller (80). The D/A converter assembly converts digital DC offset regulation signals to analog DC offset regulation signals. The summing circuit sums up the DC offset regulation signals and corresponding vectors of a received base band signal. The I/Q modulator converts the summed base band signal to a radio frequency (RF) signal. The detecting module detects an energy variation due to DC offset contained in the radio frequency (RF) signal. The microcontroller regulates the DC offset regulation signals output from the D/A converter assembly to minimize the energy variation detected by the detecting module. In the invention, the circuit saves energy and enhances qualities of communication signals.