One of the main design constraints is to prevent damages to adjacent structures, especially during excavation for basement construction. As excavation proceeds, the surrounding soils will move toward the excavation and their movement will induce bending moments and deflections in the existing pile groups. The existing pile response due to the excavation-induced lateral soil movements had been studied previously by using numerical analysis and laboratory analysis, but there are some parameters did not study up to the author's knowledge. For this reason, this research studies the interaction between existing pile groups and piles supporting excavation numerically and the effect of nearby excavation on the horizontal displacement and the bending moment of piles. Response of piles in sand subjected to lateral soil movements is studied by using PLAXIS 2D finite element software version 8.2. This research contains five groups with different cases: (1) piles supporting excavation only, (2) single-row of existing building piles, (3) double-row of capped head existing building piles, (4) triple-row of capped head existing building piles, and (5) double-group of capped head existing building piles connected by tie beam located nearby a supported excavation. A parametric study was performed to study the effect of pile supporting excavation diameter, pile supporting excavation length, excavation depth, existing building pile diameter, existing building pile length, and spacing between piles. Results indicated that excavation depth and diameter of the pile supporting excavation have the most significant effect on response (horizontal displacement and bending moment) of the pile supporting excavation. It can be said that as a result of increasing diameter of the pile supporting excavation, bending moment in the pile supporting excavation increases, however bending moments in the existing building piles decrease. Increasing diameter of the pile supporting excavation results in a minor decrease in the maximum horizontal displacements in the existing building piles, however it results in a major decrease in the horizontal displacement in the pile supporting excavation. For the existing building piles, the most significant variable parameters affecting pile response (horizontal displacement and bending moment) are excavation depth and diameter of the existing building pile. Moreover, by increasing the excavation depth, the maximum horizontal displacement and the maximum bending moment increase in both pile supporting excavation and existing building piles but that bending moment does not occur at the same depth. A closer look at the results indicates that the provision of existing building pile reduces significantly horizontal displacement and bending moment in the pile supporting excavation. Furthermore, the peripheral piles in the pile group always have higher bending moments than those of interior piles. In addition, maximum bending moment in the existing building pile in case of capped head pile group is less than that induced on a single pile at the same location.