We study the consequences of market uncertainty on international trade. An increase in foreign market uncertainty dampens China's aggregate exports on both the extensive and intensive margins. The adverse effects are more pronounced in industries facing tighter financial constraints than in others. We propose a dynamic trade model to explain the facts. Greater uncertainty depresses a firm's expected value of exporting and borrowing capacity, leading to fewer exporters and a smaller average size of exports. Under calibrated parameters, the uncertainty shock accounts for a sizable fraction of China's trade collapse in the 2008 financial crisis and the recent trade war.