To provide a method for dehydrating sludge which can solve the problem of the use of a blended flocculant, which narrows the range of application, or a problem involved in single use of a flocculant of a crosslinking polymer that requires an increased loading which raises the cost.

The method comprises adding one or more materials, selected from (a) a highly cationic and relatively low-molecular weight polymer-type water-soluble polymer, (b) a polyamidine, (c) an amine/epihalohydrin condensate, and (d) an inorganic flocculant, to sludge, mixing them together, then adding (e) a crosslinking ionic water-soluble polymer to the sludge, and mixing them together, and dehydrating the mixture.