We described the properties of microstrip band gap filter with elliptic-fractal pattern from 40 Hz to 20 GHz. It used the characteristic of the fractal and elliptic pattern to improve the performance of microstrip band gap filter. The center frequencies of gaps of the filter were about 5.5 and 15 GHz, and the band stop bandwidth of the filter can be increased by increasing the numbers of the cell of elliptic-fractal pattern. To verify the characteristic of dual-mode band gap filter, we simulated the above microstrip filter with the finite differential time-domain method. The simulation results were in good agreement with the experimental results.