The structures are subjected to additional loads due to earthquakes may lead to failures in soil and superstructure. Consequently, this research aims at studying the behaviour of large scale foundations and structures constructed on unreinforced and geosynthetic reinforced sand under seismic loads. The effect of geotextile on controlling lateral deformation of soil and decreasing pore water pressure beneath the foundation during earthquake is investigated. A two dimensional plain strain program PLAXIS (dynamic version) is used for the present numerical modeling. A ten story reinforced concrete building with basement rests on a raft foundation is idealized as two-dimensional model with and without geotextile reinforcement. A series of models for the problem under investigation were run using different numbers of geotextile layers. The effect of geotextile length is also investigated. The results indicated that the inclusion of geotextile decreased both the vertical and horizontal displacement; it significantly reduced the foundation acceleration by 72% and horizontal displacement by 63% at (N = 3), It can be concluded that geotextile reinforcement is increase subgrade stiffness and considered a good method to increase the building stability during the earthquake shaking. The lateral building deformation is reduced with the increase of length and geotextile layers number. The reduction in the building horizontal displacement and lateral acceleration were decreased by 63% and 65% respectively at (N=3).