In this paper, we propose novel omnidirectional UWB printed monopole antenna for in- body microwave imaging applications. The proposed antenna consists of a square radiating patch, a microstrip feed line and a ground plane with two resonant elements, a pair of rotated T-shaped slots and another T-shaped slot placed in the middle of the pair slots. The designed antenna provides a wide usable fractional bandwidth of more than 136.5% (2.96-15.8 GHz). This antenna has the advantages of wide bandwidth, compact size, low cost, good omnidirectional radiation patterns, and acceptable time domain behavior for using in In-Body microwave applications. The maximum measured gain for the fabricated antenna is around 6.1 dBi with an average efficiency above 89% throughout the bandwidth.