The Finance Ministry data released Wednesday showed the rate of the drop in exports to the U.S. compared to the previous year worsened from a 10.1% slip in July.
U.S. tariffs on Japanese automobiles and auto parts decreased from 27.5%, the amount Trump initially levied, to 15% this week, but that's still higher than the original 2.5%.
Wednesday's data reflect the month of August, when the tariffs were higher. Japan's overall exports were little changed, slipping 0.1%, as exports grew to Europe and the Middle East.
The provisional data for August showed Japan's imports from the world fell 5.2% from a year ago. Imports from China grew 2.1%, while exports to China fell 0.5%. Imports from the U.S. grew 11.6%.
Exports to the world grew in food, gaining 18%, as well as in ships, growing by nearly 25%. Imports grew in computers, adding nearly 35% on-year, while aircraft rose 21%.