''I have assumed this responsibility with the support of those people who want change, who want a better life, away from corruption, poverty and discrimination, people who want more respect and dignity, and hope in a secure future," Rouhani said at the ceremony Saturday.
He will formally inaugurated Sunday, but the Saturday ceremony completed the official handoff of power to Rouhani from former President Mahmoud Ahmadinejad.
The 64-year-old former nuclear negotiator, elected in June, has promised reform and to end the country's international diplomatic isolation. An Islamist activist before Iran's revolution in 1979, he is seen as having the support of the country's reform movement, the BBC said.
That movement is pressing for the release of political prisoners and the end of international sanctions against Iran because of its nuclear development program.
On Friday, as Iran marked its annual Jerusalem Day, Rouhani termed Israeli occupation of Palestinian territory "an old wound in the body of the Islamic world."