Provided is a method of producing an ink ejection head including a substrate, an ink ejection energy-generating element, a flow path-forming member, and an ejection orifice-forming member having an ink ejection orifice, the ink ejection orifice having, on a side open to an outside, a portion whose sectional area is constant and a portion whose sectional area increases from the portion to an ink ejection energy-generating element side, the method including: forming, on the substrate, a first negative photosensitive resist; forming, on the first negative photosensitive resist, a second negative photosensitive resist; partially mixing the first negative photosensitive resist and the second negative photosensitive resist to form a compatible layer; and subjecting the second negative photosensitive resist and the compatible layer to collective exposure and development to form the ink ejection orifice.