Abstract: While considering the optimization in the geometry of the leaf spring, it can be said that the design of leaf spring is quiet thickness sensitive due to its relative dimensions & the loading direction. Hence stress analysis of a mono leaf spring is done by F.E.M. before and after changing the variation of its thickness along the length. The variation of thickness considered initially is linear. After careful study it was judged that if the thickness is varied parabolically along the length of the leaf spring, better results can be obtained.