In order to achieve better heat transfer characteristics with minimum pressure penalty in a single-phase laminar flow, the shape optimization of a heat transfer surface is conducted. The present study focuses on a periodically replicated oblique wavy wall, which has recently been proposed for enhancing heat transfer with relatively small pressure loss [1]. In contrast to the previous study assuming a sinusoidal wave-form, the present study gives the degrees of freedom to all grid points at the wavy surface and their locations are simultaneously optimized based on the adjoint analysis of heat and fluid flow. It is found that the optimized shape has flattened convex and prominent peaks at the intersection of obliques waves. Such distinct features of the optimized surface greatly improves the heat transfer and pressure loss characteristics compared to the initial sinusoidal wavy surface.