A muffler for a portable engine for a chain saw or the like including separable dish shaped members having mating peripheral edges which, when interfitted one within the other, form a hollow shell. Exhaust gas inlet and outlet openings are formed in an end wall of one of the members and a deflector member is mounted exterior of the shell and is adapted to redirect the flow of exhaust gas leaving the muffler outlet openings so that the exhaust gas flows generally in the same direction as engine cooling air flow over the engine and the muffler. A shield is mounted on the shell and has a major portion spaced from the muffler shell to form a cooling air flow passage. The separable shell members, deflector, shield and a tubular diffuser disposed within the shell are held in assembled relationship on the engine by removable threaded fasteners. An engine cooling air shroud is arranged to provide for mixing of cooling air with exhaust gases passing out of the muffler before the mixture passes through an outlet opening formed by the shroud.