This paper discuss the dynamic stiffness of guideways of a ultra-precision machine tool. v-v roller guideways are employed in this ultra-precision machine tool,as they can provide very smooth motion and good straightness. Stiffness is identified from the measured data and compared with that of linear guideways. As a result, rotational vibration mode was identified from simple designed model, and its natural frequency was calculated with the designed static stiffness.