To provide a polymer flocculant drastically improving dewatering treatment efficiency of sludge by forming a firm coarse floc, in dewatering treatment of the organic sludge having undewaterability.

This polymer flocculant includes a water-soluble polymer (A) formed by polymerizing monomers containing water-soluble unsaturated monomers (a) under presence of a radical polymerization initiatior (d1) having two or more radical decomposable groups in a molecule, and having a ratio (L/η) of 1-8 between a stringing length L (mm) and an intrinsic viscosity η (dl/g).