Provided is a fiber sizing agent including a vinyl ester resin (A), an epoxy compound (B), and an aqueous medium. The vinyl ester resin (A) has an alkoxy polyoxyalkylene structure and a urethane linkage. The fiber sizing agent exhibits excellent binding ability for various fibers, such as glass fibers and carbon fibers. Molded articles produced from a molding material including the fiber sizing agent have various excellent physical properties, and examples of the physical properties include flexural strength, compressive strength, and interlaminar shear strength. Accordingly, the molded articles can be used, for example, in automotive parts, aircraft parts, windmill parts, industrial parts, and the like.