A method for defibrating a fiber body includes: a supply step of supplying a liquid to a fiber body containing fibers; and a defibrating step of defibrating the fiber body to which the liquid is supplied, and in the supply step, the liquid is supplied to the fiber body so that a rate in tensile strength of the fiber body immediately before defibrated in the defibrating step to the fiber body before the liquid is supplied thereto is 60.0% or less.