A technology capable of efficiently dissipating heat in a printing element substrate with a temperature adjustment heating element mounted thereon is to be provided. A liquid ejection head substrate capable of ejecting liquid using energy generated by an energy generating element includes: a base; a first heat transfer layer configured to be installed below the energy generating element, and formed by being laminated on the base via an insulating layer; a temperature adjustment heating element configured to be capable of adjusting the temperatures of the liquid and the liquid ejection head substrate; and a first heat transfer member configured to connect the first heat transfer layer and the base, wherein the first heat transfer member is installed between adjacent ones of a plurality of the energy generating elements and between the energy generating element and the temperature adjustment heating element.