Abstract: Cationic sizing agents for paper are manufactured by reaction of alpha-olefins with maleix anhydride, imidation of the resulting copolymer with a polyamine having at least one tertiary and one primary amino group, and quaternization of the imide with epichlorohydrin in the presence of water. Copolymers with an average molecular weight of 3000 to 30,000 are used for the conversion into imide. 1 to 50% of the amino groups of the resulting polymeric imide-amine are neutralized with an acid; after partial neutralization, the mixture is diluted with water to a 5 to 50 weight-% emulsion, then quaternized with epichlorohydrin. The sizing agent is especially suitable as a surface-sizing agent and for the sizing of paper from secondary fibers.