The Venezuelan president made the announcement hours after saying he had no doubt his country's ties with Washington would improve now that Barack Obama, the US president, was in the White House.
There was no immediate reaction from the US delegation.
The move comes nearly seven months after Venezuela expelled Patrick Duddy, Washington's top diplomat in Caracas.
Chavez expelled Duddy in solidarity with Evo Morales, Bolivia's president, who ordered out the top US diplomat in his country, accusing him of helping the opposition incite violence.
The US administration, then headed by George Bush, US president at the time, reciprocated by kicking out both nations' ambassadors.
Relations between Venezuela and the US, its key oil customer, have been frayed since Chavez came to power and positioned himself as a standard-bearer for anti-US sentiment in South America.
Chavez's announcement of better relations follows several friendly exchanges between the Venezuelan leader and Obama at the summit.
Obama met and shook hands with Chavez for the first time as the summit began.
"We shook hands like gentlemen. It was obvious it was going to happen," Chavez said after the summit opening.
"President Obama is an intelligent man, different from the previous one."
Later, Chavez presented his US counterpart with Open Veins of Latin America: Five Centuries of the Pillage of a Continent, a book by Uruguayan author Eduardo Galeano.
"This book is a monument in our Latin American history. It allows us to learn history, and we have to build on this history," Chavez said.
Obama won repeated applause at the 34-nation summit's inauguration after he promised to be an equal partner in the region and expressed his desire for a "new beginning" with Cuba.
"I think we're making progress at the summit," Obama said, after meeting with key South American leaders.
The weekend-long summit is nominally to discuss regional security and the global financial crisis, but the issue of Cuba has been much discussed.