For the vehicle of UV ink formulated with prepolymer, reactive diluent and photoinitiator, we measured viscoelasticity of film cured by UV irradiation, investigated dynamic characteristics and structural changes. As a results, it was found that equilibrium modulus and glass transition temperature are ascended, and relaxation modulus master curves are shifted toward the long time region on the curves by the increasingly exposure time. And then, it was found that flexibility tends to superiority but resistance solvent tends to inferiority by an increasing concentration of prepolymer in the vehicle