A method for producing a low-dislocation InP single crystal suitably used for an optical device such as a semiconductor laser, and the low-dislocation InP single crystal wafer are provided. In a liquid-encapsulated Czochralski method in which a semiconductor raw material and an encapsulant are contained in a raw material melt containing part comprising a cylindrical crucible having a bottom, the raw material containing part is heated to melt the raw material, and a seed crystal is brought into contact with a surface of a melt of the raw material in a state of being covered with the encapsulant to grow a crystal while the seed crystal is raised; a crystal shoulder part is grown from the seed crystal by setting a temperature gradient in a crystal growth direction to 25° C./cm or less and setting a temperature-fall amount to 0.25° C./hr or more. Thus, an iron-doped or undoped InP single crystal wafer in which an area having a dislocation density of 500/cm2 or less occupies 70% or more is realized.