The present invention provides: a carbon fiber sizing agent that can obtain a carbon fiber bundle having a superior effect of improving mechanical properties when composited using a resin; an aqueous dispersion thereof; a carbon fiber bundle; a sheet-shaped article having a carbon fiber bundle; and a composite material. The carbon fiber sizing agent contains: a compound (A) that is an ester of an unsaturated monobasic acid and an epoxy compound having a plurality of epoxy groups in the molecule, and that has at least one epoxy group in the molecule; a urethane acrylate oligomer (B) that is bifunctional and that has a tensile elongation rate of the cured product of at least 40%; and a polyurethane resin (C) having a tensile elongation rate of a dried coating film of 350-900% inclusive. The amounts of A-C contained satisfy the conditions described in the description. The aqueous dispersion disperses the sizing agent. The carbon fiber bundle contains 0.6-3.0 mass % inclusive of the sizing agent. The sheet-shaped article and a pultruded composite material contain the carbon fiber bundle. The composite material contains the sheet-shaped article.