The difference in phase and amplitude of ground motions recorded in different locations is generally known as spatial variation of seismic ground motions. This study focuses on the effects of spatial variation of earthquake ground motion on responses of adjacent buildings. The adjacent frame buildings are modeled considering soil-structure interaction (SSI) so that all the buildings can have interaction with each other under non-uniform ground motions. Based on Fast Fourier Transformation, spatially correlated non-uniform ground motions are generated compatible with known spectrum density function at different locations. Numerical analyses are carried out and the results are presented in terms of related parameters affecting the structural response using three different types of soil site classes. The results show that the effects of ground motion spatial variation are different for different site classes. The effect is more significant on rock site rather than clay site.