The present invention relates to a process for preparing an aqueous polymer dispersion comprising: preparing a dispersant co-polymer of a monomer mixture (M) by polymerising the monomer mixture (M) in a reaction medium which is substantially free from organic solvents and/or substantially free from monomers which are not soluble in water, the monomer mixture (M) comprises at least one cationic vinyl monomer (m.sub.3) and at least one monomer (m.sub.4) which is tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, or a monomer of the general formula (I): ##STR00001## wherein R.sub.1 is hydrogen or methyl, R.sub.2 is hydrogen or C.sub.1-C.sub.2 alkyl, R.sub.3 is hydrogen, C.sub.1-C.sub.4 alkyl, phenyl, or benzyl, n=1 to 4, and x=1 to 50, and then, polymerising one or more water-soluble monomers (m) in an aqueous solution of a salt in the presence of the obtained dispersant polymer. The invention also relates to an aqueous polymer dispersion, use of the dispersion and a process for the production of paper.