The two-day summit, which started on Monday, is focused on promoting regional integration, financing infrastructure projects and granting credits to small businesses that are unable to get regular bank loans.
A preferential trade agreement with Botswana, Lesotho, Namibia, South Africa, and Swaziland envisions a reduction of customs duties on 1,000 products.
Mercosur countries export around $550 million worth of goods to these states annually.
Framework agreements on the preparation of free trade treaties were signed with Turkey and Jordan. Mercosur's trade with these countries has almost doubled over the past six years.
One of the bloc's key tasks is to ensure regional food and energy supplies, which have come under pressure as Argentina and Brazil grow, Argentine Foreign Minister Jorge Taiana said.
"This summit will bring about significant steps for the integration, with the compromise of our government and all the South American governments," he said.
Another issue is new EU immigration legislation, due to come into force in 2010. The EU wants the right to detain illegal immigrants for a maximum of 18 months. Mercosur countries have condemned the new rules, which could affect Latin Americans who work in Europe and support their families by sending money home.
Founded in 1991, Mercosur unites around 250 million South Americans in a commercial free trade zone and the fluid movement of goods, people, and currency among its four member nations - Argentina, Brazil, Paraguay and Uruguay. Five more Latin American nations are associate members.