Gear vibration is caused by the mesh stiffness, gear accuracy, and assembling errors. For these reasons, helical gear has the azial, radial, and rotational vibrations. In this study, the mesh stiffness is calculated by considering the tooth bending, contact, and foundation deformations. Rotational vibration of helical gear with tooth error is modeled by the nonlidear equation of motion with single degree of freedom and is anlyzed numerically. Also, by a specially designed experimental set-up, the analysis are cross-checked and the vibration characteristics of helical gear are discussed.