To provide a dehydration method of sludge capable of obtaining the effect to or more than that of a conventional dehydration method of sludge using a plurality of flocculants and usable even in a disposal plant having dissolving tanks even in the number corresponding to one or a plurality of kinds of the flocculants.

In the dehydration method of sludge for dehydrating the sludge after an aqueous solution of a low-molecular weight anionic polymer and an aqueous solution of a cationic polymeric flocculant or an aqueous solution of an amphoteric polymeric flocculant are added to the sludge, an aqueous solution of a water-soluble anionic polymer of which the molecular weight is 1,000-100,000, preferably 1,000-10,000 is used as the aqueous solution of the low-molecular weight anionic polymer. An additional installation of a flocculant dissolving tank is not necessary, and work is easy as compared with a conventional two-pack type adding method emplying a combination of the anionic polymeric flocculant with a molecular weight of 1,000,000 or above and the cationic polymeric flocculant or the amphoteric polymeric flocculant, and it is found out that the dehydration efficiency almost equal to that of the two-pack type adding method is obtained.