The monthly business climate index calculated by Munich-based economic research institute Ifo fell to 92.9 points from 94.8 points in the previous month.
"The firms are considerably more dissatisfied with their current business situation than they were in August," Ifo president Hans-Werner Sinn said in a statement. "The downward trend in the Ifo business climate index is proceeding in large steps."
Economists polled by Dow Jones Newswires had forecast a modest drop to 94 points. A sub-index that measures the current situation fell to 99.8 points from 103.2 in August, while expectations for the coming six months dropped to 86.5 points from 87.0 points, Ifo said.