A novel planar ultrawideband (UWB) antenna with dual notched bands is proposed and investigated. The antenna consists of a square patch and a modified grounded plane. To realize dual notched bands characteristics, a T-shaped stub embedded in the square slot of the radiation patch and a pair of U-shaped parasitic strips beside the feed line is used. The advantage of this antenna is the high rejection level in the stopband. The measured results show that the proposed dual-notched-bands planar antenna shows a very wide bandwidth from 2.8 to 11.0 GHz defined by voltage standing wave ratio VSWR <; 2, with two notched bands of 3.3-4.0 GHz (WiMAX band) and 5.05-5.90 GHz (WLAN band), respectively. Both the experimental and simulated results of the proposed antenna are presented, indicating that the antenna is a good candidate for various UWB applications.