Abstract: Provided are a gas sensor element which is not prone to decreased precision of gas detection due to a decrease in temperature of a gas to be measured, and a gas sensor. An aspect of the present invention is a gas sensor element for detecting a specific gas included in a gas to be measured, the gas sensor element being provided with a solid electrolyte, a reference electrode, a measurement electrode, and a gas restricting layer. The thickness dimension WA of a portion of the gas restricting layer that is in contact with the measurement electrode, the thickness dimension WB of a portion of the gas restricting layer that is in contact with the solid electrolyte, and the thickness dimension WC of the measurement electrode satisfy the conditions WB>WA and WB?WA>WC. In a gas sensor element provided with such a gas restricting layer, the heat capacity of the gas restricting layer can be increased without hindering the gas to be measured from reaching the measurement electrode.