The vinyl ester resin sizing agents modified with epoxidized polybutadiene or epoxy terminated butadiene-acrylonitrile oligomer were prepared. The influence of the sizing agents on the performances of carbon fiber and its composite was studied. Surface topography of carbon fiber was characterized by scanning electron microscope (SEM). Fluffs and breakage, stiffness test were used to analyze the workability in later process of carbon fiber. The results indicated that the sizing agents had important influence to the carbon fiber and its composite. SEM images demonstrated that the sized carbon fiber had smooth surface. The sizing agent could significantly improve not only handling characteristics of carbon fiber due to the increase of fiber flexibility and reduction of fluffs and breakage, but also the interfacial adhesion of carbon fiber/vinyl ester resin composite.