The invention provides a gas sensor element and a gas sensor, and an electrode portion and a lead portion can be inhabited from being stripped from a joined ceramic layer. The plate-like gas sensor element extending in a longitudinal direction includes a plate-like composite ceramic layer which has an insulation portion having a through hole formed at a longitudinally forward end side and a solid electrolyte portion disposed in the through hole; an electrode portion disposed in contact with the solid electrolyte portion on a one-main-surface side of the composite ceramic layer; and a lead portion which is in contact with only the insulation portion on the one-main-surface side of the composite ceramic layer, whose forward end is recessed from the through hole toward a rear end side with respect to the longitudinal direction, and which is electrically connected to the electrode portion and extends longitudinally rearward. A rear end portion of the electrode portion overlaps with a forward end portion of the lead portion on the insulation portion on the one-main-surface side of the composite ceramic layer.