An exhaust system for a motorcycle having a catalyzer casing that is accommodated in an exhaust muffler. The exhaust muffler is provided at opposite sides thereof in the vehicle width direction with lateral walls that are inclined so as to come closer to each other as they extend downward. A bent section is formed in an intermediate portion, within the exhaust muffler, of an exhaust gas conduit passing through a front end wall of the exhaust muffler and changes the flow direction of exhaust gas from the forward and rearward direction of the vehicle to the vehicle width direction. The catalyzer casing has one end connected to a downstream end portion of the exhaust gas conduit and is arranged in an inclined condition to be lowered as it approaches one side of the muffler in the vehicle width direction.