A quasi-fractal slotted ground plane is applied to a monopole antenna for dual-frequency applications in this letter. A trapezoid patch and a quasi-fractal slot structure are printed on two FR-4 dielectric substrates as the radiator and the ground plane, respectively. The dual operating bands of the antenna are determined by the sizes of the radiator and the quasi-fractal structure. Detailed analysis is made to discuss the impact of the parameters on the operating bands for the further design. Lastly, a design example is presented and compared to a similar antenna with solid ground plane to authorize the presented technique. Its radiation characteristics are simulated and experimentally verified, and the results show that it has better dual-band performances.