A method of producing a GaN crystal is directed to growing a GaN crystal on a GaN seed crystal substrate. The method includes the steps of preparing a GaN seed crystal substrate including a first dopant such that the thermal expansion coefficient of the GaN seed crystal substrate becomes greater than that of the GaN crystal, and growing the GaN crystal to a thickness of at least 1 mm on the GaN seed crystal substrate. Accordingly, there can be provided a method of producing a GaN crystal that can suppress generation of a crack and grow a thick GaN crystal, and a GaN crystal substrate.