This article traces the decolonization of Britain’s informal empire over the teak trade in Thailand in the mid-twentieth century. It argues that British influence over the teak industry, which dated to the second half of the nineteenth century, began to wane in the 1920s due to the gradual nationalization of teak leases. Still, British firms and the Foreign Office remained dominant in the export industry in the 1920s and 1930s because of Britain’s lobbying and geopolitical authority. The Japanese invasion of Thailand in 1941 during the Second World War caused British firms to lose access to their leases and equipment. Bilateral negotiations between the Thai government and British firms after the war ended led to logs and leases being returned to British firms, but the Thai government did not renew long term leases in the 1950s despite protests from British business and government. The Thai elite looked to Americans for defense support, and they supported nationalization to expand Thai and Thai-Chinese economic authority. Britain’s military and economic authority in Thailand had eroded rapidly and, within a decade, British firms had lost control over Southeast Asia’s teak trade. This article is part of the “Crossroads of Indo–Pacific Environmental Histories” special issue of Pacific Historical Review.