A novel printed monopole antenna for ultra-wideband (UWB) applications is designed based on self-complementary structure as a matching network. The proposed antenna consists of a square radiating patch and a self-complementary structure located next to feed line, which provides a wide usable fractional bandwidth of more than 100% (3.04-11.43 GHz). Self-complementary matching network is created, by cutting two rectangular ring slots on the ground plane and by inserting two rectangular rings coupled elements in the top layer; hence, additional resonances are excited and much wider impedance bandwidth can be produced. The designed antenna has a small size of 14x22 mm(2), about 0.15 lambda x0.25 lambda at 4.3 GHz. It is shown that simulated and measured results agree well with each other and demonstrate the usefulness of the proposed antenna for UWB applications. The proposed antenna exhibits almost omni-directional radiation patterns with low cross-polarization levels and provides an acceptable gain over whole band.