The present invention relates to a method for producing a cationic surface sizing agent, and contains a first step of obtaining a copolymer (A) by solution-polymerizing a monomer mixture which contains a monomer having a tertiary amino group (a) in the amount of 15 to 45% by weight, a (meth)acrylic acid ester (b) in the amount of 15 to 85% by weight, and styrenes (c) in the amount of 0 to 70% by weight in the presence of a chain transfer agent; a second step of obtaining a copolymer (B) by polymerizing the copolymer (A) and a nonionic hydrophilic monomer (d); a third step of obtaining a copolymer (C) by polymerizing the copolymer (B) and a hydrophobic monomer (e) in the absence of a surfactant; and a fourth step of obtaining a quaternary ammonium salt of the copolymer (C) by quaternizing a tertiary amino group present in the copolymer (C).