Abstract: An aqueous liquid surface treatment composition having a pH value not more than 6.5 and containing phosphoric acid ions, condensed phosphoric acid ions, an oxidizing agent, and a water-soluble polymer consisting, except for end groups, of polymer units expressed by formula (I), in a weight ratio of 0.1 to 30:0.1 to 10:0.1 to 10:0.1 to 20 respectively, when brought into contact with an aluminiferous metal surface, rapidly forms on the surface a conversion coating that has good corrosion resistance and adhesion to subsequently applied organic coatings such as paint and is less easily damaged by mechanical stresses than prior art conversion coatings.