Abstract: A simple boundary element approach for the system of circular piles and soils is formulated to predict the lateral impedance and kinematic seismic responses of fixed-head pile groups during the lateral vibration or seismic excitation. The dynamic interaction of piles in a group and the passive pile effect are considered in the dynamic equilibrium of a pile foundation. The elastic solution to the lateral impedance and kinematic seismic responses of the massless pile cap, restricting against rotation, is obtained in the frequency domain. The results show that the soil-displacement-influence coefficient can be used to consider the pile-soil interaction along a pile and to capture the kinematic bending moment accurately. Meanwhile, the coefficients provide reasonable estimations of the lateral impedance and kinematic seismic response of pile groups.