The elastic properties and breaking strength do not remain constant and vary nonlinearly under cyclic thermal loading. The variation is larger and indeed more important in the case of composites as compared to isotropic materials. The variations of strength and elasticity modulus may be represented as a function of the number of thermal shocks, i.e. the difference among the temperatures exerted in these cycles and a reference temperature; which are measured experimentally. A new experimental device is designed and manufactured which can be conveniently used to apply thermal loads with different temperature on composite laminates. Subsequently, orthotropic glass-epoxy composites made by hand lay-up are tested under cyclic thermal loading using this apparatus. The variation of the elasticity modulus and breaking stress of the samples are measured before and after exerting defined number of thermal load cycles. As a result a convenient mathematical model is proposed whose predictions are in agreement with the experimental measurement. Finally, the obtained equations are used as the representative of material behavior in an analytical study of laminate fracture. The result show that nonlinear behavior of the composite under the thermal shock affects the breaking strength.