She took over from her mentor, Luiz Inacio Lula da Silva, who stepped down after two terms as the most popular president in the country's history.

Ms Rousseff was appointed energy minister in President Lula's government in 2003 and served as his chief of staff from 2005 to 2010.

She was elected in October, defeating the opposition candidate Jose Serra by 56% to 44% in a run-off vote.

After swearing the oath of office, Ms Rousseff began her inaugural address by noting that this was the first time in Brazil that the role of president had been given to a woman.

"I know the historical significance of this decision," she said to widespread applause. "Today, all Brazilian women should feel proud and happy."

She also outlined her plans for tax reforms, environmental protection, improved health services, regional development, and measures to protect the economy from foreign "speculation".

During President Rousseff's term, Brazil will host the Rio Plus 20 global environmental summit in 2012 and the Fifa World Cup in 2014. She will also oversee preparations for the Summer Olympics in 2016.