Provided is a liquid ejection head substrate having a base, a heat generating resistor layer formed on or above the base and including an electrothermal conversion portion, a wiring electrically connected to the heat generating resistor layer and defining the electrothermal conversion portion and a protecting film covering at least the electrothermal conversion portion and the wiring of the heat generating resistor layer. In the liquid ejection head substrate, the wiring is made of an alloy containing Al as a main component and Cu and having an average crystal grain size of 300 nm or less.