The leader of the African National Congress (ANC) party promised to boost the country's economy and clean up corruption during the massive ceremony at Loftus Versveld Stadium in the administrative capital, Pretoria.
Over 32,000 people, including several government officials and African heads of states, attended the ceremony. Among the guests were the Presidents of Namibia, Zimbabwe, Tanzania and the Democratic Republic of Congo.
"I am humbled by the trust you have bestowed upon me, aware of the challenges our country faces, but also alive to the fact that our people are filled with hope for a better tomorrow," Ramaphosa said during his inaugural speech.
He was formally re-elected President on Wednesday after lawmakers backed him during an election at Parliament's National Assembly, which is responsible for selecting the South African President, Efe news reported.
The 66-year-old leader's election came after the ANC won the May 8 polls with 57.5 per cent of the vote.
"Despite our most earnest efforts, many South Africans still go to bed hungry, many succumb to diseases that can be treated, many live lives of intolerable deprivation. Too many of our people do not work especially the youth," Ramaphosa said.
He encouraged the nation to build a better society for the new generation, without racism or sexism.
Ramaphosa, who came to power in February 2018 when his ANC predecessor Jacob Zuma caved in to party pressure amid a corruption scandal, will now take on his first full five-year term.
The ANC, the party of late leader Nelson Mandela, has been in power since the end of apartheid in South Africa.
It won its sixth consecutive election with 230 out of 400 seats in the elections, which is the lowest-ever vote share for the ANC.
( With inputs from IANS )