The agency said its decision was taken because of "increased risk of further shocks emanating from the euro area debt crisis," and the banks' inability to compensate for losses.
"Moody's Investors Service has today taken various rating actions on seven German banks and their subsidiaries, as well as one German subsidiary of a foreign group," a Moody's statement released Wednesday said. "As a result, the long-term debt and deposit ratings for six groups and one German subsidiary of a foreign group have declined by one notch, while the ratings for one group were confirmed."
Frankfurt-based Commerzbank was reduced from a rating of A2 to A3, while a review of Deutsche Bank, Germany's largest lender, will conclude later.
Other banks to be downgraded included Unicredit Bank, DekaBank, DZ Bank, as well as Landesbank Baden-Württemberg and Norddeutsche Landesbank - all with stable looks.
Moody's also affirmed WGZ Bank's rating at A1, but with a negative outlook.
But Moody's also underlined that the ratings of German banks have declined by less compared to other European banks, because of relatively good conditions in Germany's domestic banking market, low unemployment, and low household and corporate debt levels.