Hillary Clinton, the US secretary of state, placed second, followed by Brazilian President Dilma Rousseff, making the top three spots unchanged from last year.
The list named women involved in policymaking, entertainment, technology, and non-profit organisations, among other fields. They were ranked according to influence, the amount of money they control or earn, and media presence.
“These power women exert influence in very different ways and to very different ends, and all with very different impacts on the global community,” said Moira Forbes, president and publisher of ForbesWoman.
The magazine noted Merkel’s resolve in preserving the EU and her influence over the eurozone’s ongoing debt crisis.
Clinton was applauded for her handling of crises such as the release of a trove of diplomatic cables by the anti-secrecy group WikiLeaks.
Forbes cited Rousseff for her leadership of the world’s eighth-largest economy and approval ratings within her country.
The average age of the 100 power brokers from 28 countries was 55. They had a combined 90m Twitter followers, Forbes said.
Also in the top five were Melinda Gates, co-chair of the Bill & Melinda Gates Foundation and wife of Microsoft co-founder Bill Gates, and Jill Abramson, the executive editor of the New York Times.
Sonia Gandhi, president of the Indian National Congress, followed at No 6.
US first lady Michelle Obama, who had topped the list in 2010, was in seventh place.
The list featured newcomers such as actress and performer Jennifer Lopez and the billionaire phil-anthropist and widow of Apple founder Steve Jobs, Laurene Powell Jobs.
Republican US Representative of Minnesota and former White House hopeful Michele Bachmann was among 21 women who fell off the list this year.
Christine Lagarde, the managing director of the IMF, was in eighth position. The former French cabinet minister has been on the list since it began in 2004.
“So many of these women are in policy or political roles, and their influence... is only growing so it’s not surprising that someone like Merkel or Clinton would continue to be present on the list year to year,” said Forbes.
* The full list is available at www.forbes.com/power-women