Thermal deformation of cast iron exhaust manifold for turbo diesel engine is investigated by finite element analysis (FEA). The FE model includes the temperature dependent material properties as well as the interactions between exhaust manifold, cylinder head and fasteners. It also considers the sliding behavior of the flanges of exhaust manifold on cylinder head when either expansion or contraction of the exhaust manifold exceeds the fastener pretension. The result of analysis revealed that remarkable thermal deformation occurred along the longitudinal direction. The amount of deformation was predicted and compared with experimental results. The new design of fastener hole, which allows sliding behavior, is expected to reduce thermal stress in turbo diesel engine exhaust manifold.