Abstarct: Due to the heterogeneity of the soil environment, soil properties vary from one point to another. This variability can affect the results of analysis. The main objective of this research is to investigate the effect of soil uncertainty on the seismic fragility of piled raft supported structures considering soil-structure interaction. In this study, the internal friction angle, cohesion and shear modulus of soil are considered as random variables, using a code written in MATLAB, the values of these two parameters are calculated for all points in the soil environment using random field theory. In the next stage, the soil environment, pile group, raft foundation, and a 10-story reinforced concrete structure with special moment frxame are modeled in the OpenSEES software. Incremental dynamic analysis is performed on the model using two near-field and two far-field earthquakes. By comparing the obtained outputs for homogeneous and random soil, the effect of soil uncertainty on these outputs, including pile lateral displacement, IDA curves of roof lateral displacement and maximum structural drift and fragility curves, are investigated. The length of the piles, the covariance of the internal friction angle, soil cohesion and shear modulus of soil are parameters that have different values in the constructed models. By examining the results, it is evident that, in general, considering soil uncertainty leads to an increase in lateral displacement of the piles, roof displacement, maximum structural drift, and the probability of structural failure in fragility curves.