Abstract: In this paper,a semi-analytical method to calculate the response of pile groups embedded in a layered soil to arbitrary incident seismic waves is presented. The plane-strain assumption used for dynamic analysis of pile foundations is abandoned and Kausel's dynamic Green function is used to form the flexibility matrix of soil. The pile is modelled by beam elements and the arbitrary incident seismic waves is applied to the primitive input motion of pile foundations.The results of a numerical study on the behavior of pile groups embedded in a layered soil subjected to vertically and obliquely incident SH,SV, and P waves are presented.It is shown that the method developed in this paper has the advantage of high accuracy in the lower frequency range and less computational time.