In this paper, the design of microstrip patch antenna fed by Halfmode Substrate Integrated Waveguide (HMSIW) is presented. The proposed microstrip patch antenna is placed at an inset in the open end of the HMSIW separated by a narrow slot. The HMSIW is excited to generate dominant TE10HM mode. The amount of inset of the patch in the HMSIW helps to get impedance matching and as a result, the incident wave couples easily from HMSIW to patch antenna. The proposed antenna resonates at 10.5 GHz with the bandwidth of 500 MHz (4.76%) and cross polarization level lower than -21dB. © 2015 IEEE.