Feed drive system of machine tools may experience serious vibrations or unstable motions during high-speed operation. In this paper, a 6 D.O.F (Degree-Of-Freedom) lumped parameter model was proposed in order to analyze vibrations of a ball screw feed-drive system, which takes planar motion. The equations of motion were derived for the proposed model. Natural frequencies of the system and transient responses due to driving motor speed control input were also analyzed. Experimental modal analysis and operational vibration measurements of a laboratory ball screw feed drive system were made. Both theoretical analysis and experimental measurement results showed good agreement with each other. Consequently we concluded that the proposed 6 D.O.F model could be well applicable to the vibration analysis of a ball screw feed-drive system.