A gas sensor includes a gas sensor element, a metallic shell, and a tubular protector fixed at a front side of the metallic shell. A front end of the gas sensor element faces an internal space formed between an inner surface of the protector and an inner surface of the metallic shell. The protector includes: a fixing portion surrounding the front side of the metallic shell and fixed to the metallic shell; a space partition portion extending radially and having inner gas introduction holes communicating with the internal space; a side wall connected to a radially inner side of the space partition portion; and a bottom wall formed on a front side of the side wall with an inner gas discharge hole. The gas sensor element is located rearward relative to an inner surface of an inner gas introduction hole located on the frontmost side.