Structural models and their related parameters, are most often considered as deterministic, in numerical analysis. However, according to test results, one can see the existence of uncertainties, in most cases, due to various reasons, such as, natural variabilities and ignorance. Thus, dealing with uncertainty has gained massive attention, due to its importance in structural analysis and anticipating the performance of models. In fact, in some cases of special structure components, like glue laminated timber beams, it appears to be, that there is an absence of information concerning uncertainties. Therefore, the main objective of this study is to inspect uncertainties that facing designers and their role in glue laminated timber beams behavior, by considering different material parameters as random variables. In addition, four-point bending tests are conducted and finite element analysis is conducted, using ABAQUS software, to model the nonlinear behavior of GLT beams. For purposes of numerical model calibration, Hill yield criterion constitutive model is considered based on the obtained data from the experimental test. The results of this study provide a better outline for understanding the effect of uncertainties on glue laminated timber beams.