The flash estimate for the 27 EU countries came to a reading of minus 22.6 from minus 20.2 in July.
For the 17-member eurozone, the confidence indicator dropped from minus 21.5 in July to minus 24.6 in August, the commission said.
Concerning a drop in the Economic Sentiment Indicator from 90.4 to 89 in the European Union and from 89.9 to 87.9 in the eurozone, the commission said the largest decline in the European Union came from shrinking confidence in the service sector.
"The decline resulted from lower confidence in all sectors entering the calculation of the ESI," the commission said. "However, a loss of confidence in the services sector was the main driver of the decrease in the EU, while the euro area saw the biggest declines in industry and among consumers," the report said.