Attitude determination is essential for navigation of land vehicles, but the inertial sensors used for attitude estimation are susceptible to environmental disturbance. In this paper, vibrational influences on inertial sensors are analyzed. A method to use single-antenna GPS for pseudo-attitude estimation is presented. Then, an extended Kalman filter is proposed for data fusion. Results shown that the proposed method can determine attitude with vibration on land vehicles and estimate the acceleration well, compared with the complementary filters.