Forbes said Obama topped the list this year because "she has made the office of first lady her own" while remaining popular.
She's effective in response to her Let's Move! campaign against childhood obesity, companies like Coca-Cola, Kellogg and General Mills have pledged to reduce the calorie content of their foods by 2015," Forbes said.
Kraft Foods Chief Executive Irene Rosenfeld, who led a hostile billion takeover of Britain's Cadbury, came in second, followed by media mogul Oprah Winfrey, who is set to launch her cable network OWN.
German Chancellor Angela Merkel who won top in 2009 came to fourth place and Hillary Clinton who was put in charge of Middle East peace, rounded out the top five. PepsiCo Inc Chief Executive Indra Nooyi was in sixth rank while Lady Gaga came in the 7th place.
Gail Kelly, chief executive of Australia's Westpac Banking Corp, was in eighth place, followed by singer Beyonce Knowles. Talk show host Ellen DeGeneres rounded out the top 10.