"I'm not a doctor but I can say that from what he was a few days ago there is great improvement," Winnie Madikizela-Mandela told reporters outside his former home in Orlando, Soweto.
Madikizela-Mandela called on the media not to "get carried away" in their reporting on her former husband's illness.
"Please understand the sensitivities and the feeling of the family," she said.
"It can also happen that you have crossed the boundaries."
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Mandela, who turns 95 on July 18, has been admitted to a hospital here on June 8 with a recurring lung infection.
Well-wishers are continuing to gather outside the hospital where Mandela, regarded the founding father of South Africa's multiracial democracy, was admitted 21 days ago.
They have been singing and saying prayers outside the hospital and at Soweto former home of Mandela, who is revered across the globe as a symbol of resistance against injustice.
South African children released 94 balloons - one for every year of Mandela's life - into the air in his honour.
Mandela had a long history of lung problems, dating back to the time when he was a political prisoner on Robben Island during apartheid. While in jail he contracted tuberculosis.
Mandela is revered for leading the fight against white minority rule in the African country and then preaching reconciliation despite being imprisoned for 27 years.
Mandela served as the country's first black president from 1994 to 1999.He left power after five years as president.
He retired from public life in 2004 and has not been seen in public since the football World Cup finals in in 2010.
Meanwhile, South Africans protested against Obama's visit to the country. Trade union activists, students and South African Communist Party cadres staged the demonstration to protest Obama's "arrogant, selfish and oppressive" foreign policy.