"The traditional wedding of President Jacob Zuma and Tobeka Madiba tomorrow, 4 January, is a private family ceremony," the presidency said in a statement.
The Sunday Times and Independent newspapers reported Zuma's homestead in Nkandla was a hive of activity this week as he prepared to tie the knot with Madiba on Monday.
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"Most of the things are only happening from (Sunday). We are expecting the arrival of a number of guests and dignitaries.
"There is obviously a lot of dancing and singing at the moment - people are happy. But tomorrow (Monday) is the big day," the Independent said, citing a source close to the family.
Plans to marry sixth wife
Monday's wedding ceremony will be a traditional one, in which the bride will be introduced to the elders as well to the ancestors two years after Zuma paid an Ilobolo (dowry).
Madiba, 37, who has two children with 66-year-old Zuma, has attended official functions as one of the country's first ladies and has been quoted in the media as Thobeka Madiba-Zuma.
Polygamy is legally recognised in South Africa.
According to a biography on Zuma prepared by his party, the African National Congress, the president has three wives, including Madiba, but details on their marriage remained vague.
Meanwhile, Zuma is also reportedly preparing to take on a sixth wife.
Earlier this week, an umbondo (exchange of gifts) ceremony was held signalling he had paid ilobolo (dowry) for his latest fiancee, Bongi Ngema, the Sunday Times reported.
Ex-wife named cabinet minister
When Zuma was inaugurated as head of state in May, speculation was rife about who would be the first lady.
He attended the ceremony with his first wife, Sizakele Khumalo, whom he has known for 50 years and married in 1973.
Zuma is also married to Nompumelelo Ntuli Zuma. They wed in 2008 in a lavish ceremony.
One of his earlier wives, Kate Mantsho Zuma, committed suicide in 2000.
In 1998 he divorced Nkosazana Dlamini-Zuma, but she remains in his inner circle as she is the home affairs minister.
