An all-textile substrate integrated waveguide (SIW) cavity-backed circular ring-slot antenna for wireless body area network applications is proposed. The antenna consists of an SIW cavity-feed structure and a circular ring slot. The excited electromagnetic energy is radiated by the circular ring slot. All components of the antenna are made from textile materials. A two-thirds muscle-equivalent phantom was used to analyze human body effects. The performance of the antenna was not significantly affected by antenna deformation or the human body due to the SIW cavity-backed feed structure. The antenna had overall dimensions of 75 × 42 × 1 mm3. The measured 10-dB return loss bandwidth of the antenna on the phantom fully covers the 5.8-GHz Industrial, Scientific, and Medical Band.