In a statement, the authority, known as Bundeskartellamt, said the fine had been imposed because the American software company had "influenced the resale price of the software package 'Office Home & Student 2007' in an anti-competitive manner."
It said the product had been heavily advertised in in retail stationary outlets during the autumn of 2008 .
"Amongst others, a nationwide active retailer advertised the product with financial support from Microsoft," it said.
"Even before the launch of the advertising campaign in mid-October 2008, employees of Microsoft and the retailer in question had agreed on at least two occasions on the resale price of the software package."
The authority added that contacts between supplier and retailer regarding resale prices should not lead to co-ordination where the supplier actively tried to co-ordinate the pricing activities of the retailer and the retailer and supplier agreed on the retailer's future actions.
"In the present case, this boundary has been crossed," it said, adding that Microsoft had accepted the fine.