A sensor element for a gas sensor includes: an element base being a ceramic structure including a sensing part to sense a gas component to be measured; and a leading-end protective layer being a porous layer to surround a predetermined range from a leading end portion on a side of the sensing part of the element base. The leading-end protective layer protrudes at a first end portion thereof opposite to a portion surrounding the element base in a longitudinal direction of the element base. A/B≥1.1 where A is maximum thickness of the leading-end protective layer, and B is thickness of the leading-end protective layer in a base portion that does not protrude.