Abstract— Implantable antennas have many important healthcare applications. One key aspect for a successful communication process from the implantable device to the on or off-body receiver is the accurate evaluation of the in-body path losses. These losses include, mainly, the attenuation and the reflection losses. Usually, normal incidence is considered for the calculation of the reflection losses between the tissue layers. However, this is not very accurate as the incident wave may be oblique at the boundary between the tissue layers. Therefore, in this paper the influence of oblique incidence on the reflection losses in a multilayer human body model is investigated. The reflection losses at the bone/muscle, muscle/fat and fat/skin layers are calculated at 403 MHz considering the cases of parallel and perpendicular polarization oblique incidence. The results are analyzed and compared with those of normal incidence. They show that larger losses are obtained at some angles for the case of oblique incidence compared to those for the case of normal incidence (about 241.16% larger reflection loss is obtained at an incident angle of 85° for the case of oblique incidence/perpendicular polarization at the fat/skin interface in comparison with that for normal incidence). Hence, it is very important to take the oblique incidence into consideration to provide more accurate in-body path loss calculations.