To obtain a water-soluble vinyl polymer having a high thickening capability to a salt water solution and exhibiting a high aggregating power by subjecting a specified vinyl monomer and another water-soluble vinyl monomer to copolymerization.

This water-soluble vinyl polymer is a copolymer consisting of (A) a vinyl monomer as expressed by the formula CH2=C(R)-COOZ1(O)pZ2OX (R is a hydrogen atom or a methyl group; Z1 and Z2 are each 8 or more C alkylene groups; X is a 4 or less C hydrocarbon group; (p) is an integer of 0 or 1) and (B) another water-soluble vinyl monomer and has an intrinsic viscosity of 4 or more measured at 30°C in 1N-NaNo3. Preferably B is an inexpensive acrylate. Preferably the number of mols of A is 10-90% of the total number of mols of A and B.