The elastic behavior of gold thin films deposited onto Kapton substrate has been studied using in situ tensile tester in a four-circle goniometer on a synchrotron beam line (LURE facility, France). The mechanical description of the substrate-thin film composite structure has been developed to determine the stress tensor in the film while the strong {111} fiber texture was taken into account using the crystallite group method (CGM). CGM strain analysis allowed us to forecast the nonlinear relationship between strain and sin2 Ψ obtained for the thin films due to the strong anisotropy of gold. A least-square method was used to fit the overall experimental data with good accuracy and allows determining all single-crystal elastic constants.