Mineral ore slurry pretreatment method, and method for manufacturing mineral ore slurry

There is provided a method capable of effectively reducing the amount of acid used in a leaching step and the amount of a neutralizer used in a final neutralization step while nickel yield in a hydrometallurgical process for nickel oxide ore is not reduced. A method for pre-treating ore slurry according to the present invention is a method for pre-treating ore slurry to be provided to a leaching treatment in a hydrometallurgical process for nickel oxide ore, the method including: a first separation step for separating ore slurry into a coarse particle fraction and a fine particle fraction; a second separation step for separating the coarse particle fraction separated in the first separation step into a heavy specific gravity fraction and a light specific gravity fraction; and a vibration sieving step for separating, by a vibration sieve, the light specific gravity fraction.