There is no consensus on the existence of welfare gains from international monetary policy cooperation. This study adds to the debate by providing a new open macroeconomics model with incomplete exchange rate pass-through. We find that, from a global perspective, the welfare gains from international monetary policy cooperation arise with incomplete exchange rate pass-through. Furthermore, the country’s incentive for cooperation increases with its degree of exchange rate pass-through. Cooperation benefits small countries with high pass-through; however, it is disadvantageous to large countries with low pass-through. In addition, when there is in the absence of cooperation, fixed exchange rate regime is preferred for a country suffering from monetary uncertainty, particularly for small economies with high exchange rate pass-through.