A multiband printed monopole antenna applied to WLAN/WiMAX applications is designed. The top of the antenna is composed of three strips and the bottom is a defected ground structure used to improve the impedance matching of the antenna. The antenna was simulated by using a three-dimensional electromagnetic simulation software (Ansoft HFSS13.0), and it was fabricated on a substrate with teflon material. The sample of the presented antenna was connected to a test equipment (Agilent Technologies N5230C 10 MHz-20 GHz) for testing via an SMA adaptor. The measured result is consistent with the simulated result, which verifies the correctness of the design.