Disclosed are: nickel complex hydroxide particles that have small and uniform particle diameters; and a method by which the nickel complex hydroxide particles can be produced. Specifically disclosed is a method for producing a nickel complex hydroxide by a crystallization reaction, which comprises: a nucleation step in which nucleation is carried out, while controlling an aqueous solution for nucleation containing an ammonium ion supplying material and a metal compound that contains nickel to have a pH of 12.0-13.4 at a liquid temperature of 25° C.; and a particle growth step in which nuclei are grown, while controlling an aqueous solution for particle growth containing the nuclei, which have been formed in the nucleation step, to have a pH of 10.5-12.0 at a liquid temperature of 25° C. In this connection, the pH in the particle growth step is controlled to be less than the pH in the nucleation step.