The attitude of France towards the Sino-Japanese War that started in 1937 has given rise to various judgments. Officially neutral, France is often presented as having taken, at least morally, a favorable attitude toward China. Yet the French government had officially prohibited the transit of war materiel en route to China across the Indochinese border. This issue became increasingly important as the Japanese blockade of China progressed and conditioned the capacity of Chiang Kai-shek’s government to continue the fight. The diplomatic archives of the United States, greatly concerned by the situation in China, shed more light on France’s policy in East Asia. By comparing historical accounts produced by contemporaries and historians with the diplomatic archives of the United States, this article intends to bring more evidence relating to the issue of French “neutrality” during the Sino-Japanese War.