A novel hexagon slot antenna which operates at Industrial, Scientific, and Medical(ISM) band is proposed. The simulation results of method of moments based on full wave analysis indicate that the bandwidth of the proposed antenna increases from 30% to 48.5%(|S11|<-10 dB)compared with a traditional square slot antenna. The |S11| of the fabricated antenna is measured. The radiation patterns at 5.24 GHz, 5.8 GHz and 8.59 GHz, which are the initial frequency, resonance frequency and cut-off frequency of the passband, respectively, are measured in a microwave chamber as well. The measured results agree well with the simulation results. This work provided a novel method to broaden the bandwidth of microstrip slot antenna.