Merkel, who had held the number one spot for four years, dropped down to fourth place in the 2010 Forbes list, which is to be published Thursday.
Merkel came behind runner-up Kraft Foods Chief Executive Irene Rosenfeld and the third-placed US media mogul and talk-show queen, Oprah Winfrey.
However she squeezed out US Secretary of State and former first lady Hillary Clinton in fifth place.
The German Chancellor is widely thought to have had a mediocre year, despite being re-elected with a strong mandate last September. Her plunge in the power rating is likely to stem from the perception that under her leadership, Germany has stepped back from its traditional leadership role in Europe to focus more on national priorities.
In its brief profile of Merkel, Forbes made note of the persistent quarrelling within her coalition government.
The list of the 'World's 100 Most Powerful Women' also included corporate honchos such as India-born Pepsi Co chief Indra Nooyi and heads of state such the Queen of England.
The only other German woman on the list was former model, Heidi Klum, in 39th spot.