South Africa and the Democratic Republic of the Congo have signed two key political and business agreements.
This is the first visit by a South African leader to DR Congo
One deal, signed in Kinshasa by visiting South African President Thabo Mbeki, will help DR Congo rebuild its political system and tourism industry.
Business leaders from both countries have also signed a cooperation pact that will set up joint ventures, particularly in mining.
South Africa helped broker the end of a war that claimed some 2 million lives.
The BBC's Arnaud Zajtman in Kinshasa says under the mining agreement, a South African company will produce gold worth $8bn in DR Congo within a period of between 10-15 years.
President Mbeki is accompanied by a large delegation, including more than 20 business executives and six senior government ministers on his first state visit to DR Congo.
Later on Wednesday, President Mbeki and his DRC counterpart Joseph Kabila signed a wide-ranging co-operation pact.
It calls for the two countries to work together in many fields - including security, politics, economics, human rights , education, and tourism.
South Africa also agreed to inject S10bn into the DRC.
Before signing the deal the South African leader addressed parliament where he stressed the need to rebuild the country after five years of war.
"We need a renaissance, a reconstruction, a rebirth of
Congo," President Mbeki told DR Congo's parliament.
Mr Mbeki held talks with Mr Kabila's four vice presidents, two of whom are former rebels, to evaluate progress in consolidating peace.
Meanwhile, the United Nations envoy to DR Congo has said that it is possible "on a technical level" to hold elections next year as planned.
However William Swing said it depended on the political will, which was "less certain".
Some observers had said it would be logistically very difficult to organise elections in DR Congo, due to the lack of infrastructure such as roads in many parts of the vast country, which is the size of western Europe.
DR Congo has enormous deposits of gold, silver, diamonds, copper, cobalt, zinc and uranium, but much of the mining sector has collapsed after mismanagement, and looting.
South Africa has advanced mining technologies, which could be used to exploit this untapped wealth.
Since the end of apartheid in 1994, South African companies have vigorously expanded into many African countries, in sectors such as retailing and communications.