TEHRAN, Young Journalists Club (YJC) - Foreign heads of state from more than 40 countries were among 36,000 people who witnessed the event replete with pomp, military honours and an airforce flyover at a rugby stadium in Pretoria.
The 66-year-old leader was unanimously elected by parliament to a five-year term after his African National Congress (ANC) won legislative elections on May 8, taking 230 of the 400 seats.
The ANC garnered 57.5 percent of the vote, its weakest result since apartheid was overturned 25 years ago.
Ramaphosa is a trade unionist who played a prominent part in the struggle to end white-minority rule before becoming a successful businessman.
He faces a herculean task to tackle the country's many problems - from a sickly economy in which more than a quarter of the workforce is jobless, to entrenched crime and corruption and land ownership that remains overwhelmingly in the hands of whites.
Many solutions will require him to inch his way along a high wire, balancing leftwing calls for radical change with investors' demands for caution.
"A new era has dawned in our country. A brighter day is rising upon South Africa," Ramaphosa said in his inaugural address.
"This is a defining moment for a young nation like ours. It is a time for us to make the future that we yearn for.
"I pledge here today that I will serve you ...to build the South Africa that we all want and deserve.