The monthly ZEW poll of Germany's financial sector showed a fall to an indexed 14.1 points in March from 15.7 points in February, a statement said.
Around 40 percent of the results in Europe's biggest economy were received as or after the Japanese earthquake, tsunami and nuclear crisis occurred, but all the opinions were collected before the full extent of the crisis had emerged.
"The German economy is in a robust shape. Nevertheless, the tragic events in Japan could slow down the dynamics of German economic growth at least in the short run," the statement quoted ZEW president Wolfgang Franz as saying.
Overall however, "the indicator shows that financial market experts continue to expect a positive economic development during the forthcoming six months," it added.
Analysts polled by Dow Jones Newswires had expected the index to remain unchanged.
ZEW said that "the current survey period covered two major events," a hint by the European Central Bank that it would raise its main interest rate next month, and the Japanese catastrophe which has slammed global stock markets.
The overall indicator, which measures financial market expectations, is well below its historical average of 26.7 points.
Citi analysts said in a research note however that "we do not expect the earthquake to overwhelm world economic recovery or investors' risk appetite."
A measure of how German investors view the situation at present edged higher meanwhile, gaining 0.2 points to 85.4 points, which was nonetheless lower than an analyst forecast for a rise to 86 points from from 85.2 in February.