The welded structures have a broad applicability in automotive industry. The welding being an assembled process, presents both advantages and disadvantages for the two wheeler motor structure. A simple existing defect after welding can generate a catastrophic fracture. Recently all major fabricated structures in two wheelers are optimized by Computer Aided Engineering - Finite Element Analysis techniques to meet the constricted weight to strength and stiffness targets. Local reinforcements in the main structure with unequal member thickness are playing major role to meet these requirements. Various critical parameters which affect the weld structure life are not being modeled in FE analysis to minimize the modeling complexity and computation times. But in FEA-simulations acceptance stress values for a given base material are derived as a function of various parameters like the geometry, size, thickness, weld location, weld toe, flank angle, welding quality and cold working process etc. In this paper the effect of the base material thickness and weld location on fatigue life of welded structure and FEA simulation acceptance limit values are investigated for two wheeler scooter frame. In order to predict the fatigue behavior of the welded structure, a constant amplitude loading is applied where the influence of the thickness ratio over the fatigue life and acceptance values for same base material are presented.