A novel folded ridge substrate integrated waveguide (FRSIW) is proposed, and the design of a higher-order-mode bandpass filter in FRSIW technology is presented. The FRSIW is proposed by folding a typical RSIW. It has a size nearly half of the conventional RSIW while keeping a relatively wide single-mode bandwidth. A higher-order-mode bandpass filter is designed and tested based on the TE201 mode in the FRSIW. The measured frequency responses show that the proposed FRSIW filter has good selectivity, low loss and compact size.