In this paper, based on the detailed analysis of the dynamic cutting force of the helical tooth end milling cutters and its direction coefficients, a method of analysing the behaviour of regenarative chatter for helical tooth end milling cutters with waved cutting edges is proposed.The cutting tests are carried out to check the theoretical analysis on validity and they have proved to be in good agreement with the results calculated from the theoretical analysis. The results obtained are summarized as follows: 1. The proposed theoretical formulae for the calculations of instantane -ous and mean direction coefficients can be applied to up- and down- milling operations with helical tooth end milling cutters. By using these formulae the relations between the chatter and cutting conditions can be found, which enables us to select the optimum cutting conditions easily. 2. The equation which can be applied to the determination of the critical width of cut for helical tooth end milling cutters with waved cutting edges is given below: Where: Kd is the coefficient of chip thickness, b is the critical width of cut, D is the equivalent damping ratio, K is the equivalent static stiffness, Rm is the mean direction coefficient, Z is the number of teeth, ¦× is the phase shift between the two vibration waves in successive cutting teeth, ¦Î is the ratio between the length of the chip and the lead of the waved cutting edges, ¦Çi, ¦Ç2, ¡¡,¦Çz are the ratio between the partial length on the underside of the chip and the length of the chip respectively. 3. It is dear from the theoretical analysis and the experimental results th at the critical width of cut for the helical tooth end milling cutters with waved cutting edges is considerably larger than that of the conventional milling cutters. Practically, this method of analysis can also be applied to the determination of the chatter behaviour for the helical tooth end milling cutters with any kinds of grooves on the cutting edges and it may be expected o obtain the similar results mentioned above.