A liquid ejection head substrate includes a heating resistor array including a plurality of heating resistors and a protective film covering at least one of the heating resistors. The liquid ejection head substrate further includes a supply opening array and an electrode. The supply opening array is disposed on a side of a surface of the liquid ejection head substrate on which the protective film is provided. The supply opening array includes a plurality of supply openings through which a liquid is supplied arranged in a direction along the heating resistor array. The electrode is disposed on the side of the surface in a space between the supply openings adjacent to each other in a direction along the supply opening array. The electrode is configured such that a voltage is applied between the electrode and the protective film.