Hugo Chavez and Mahmoud Ahmadinejad have met several times
Iranian President Mahmoud Ahmadinejad is in Venezuela on the third leg of his tour of South America to boost ties.
He is set to sign business and industrial accords with his close ally, Venezuelan President Hugo Chavez.
Mr Chavez, who has said he wants to develop nuclear energy, has backed Iran's right to a nuclear programme.
The Iranian leader arrived from Bolivia where he and President Evo Morales stressed the right of all nations to a peaceful nuclear programme.
President Ahmadinejad was assured of a warm welcome from his Venezuelan host, Hugo Chavez.
The two outspoken critics of the US have visited each other several times and co-operation between their countries has grown in recent years.
"We have a solid foundation, a solid base that we have created over this decade in our relationship, and it shows how false are the attacks of the world empire," said Venezuelan Foreign Minister Nicolas Maduro.
The two men are expected to sign some 270 agreements in fields such as agriculture, industry, technology and energy during Mr Ahmadinejad's visit.
Opposition parties and Venezuela's Jewish community expressed opposition to the presence of the Iranian president.
Former deputy foreign minister Adolfo Tayllardhat told BBC Mundo that the deep ties were just between the two leaders.
"We've lost count of the number of accords signed between Chavez and Ahmadinejad. But I insist these are just personal relations, not between Venezuela and Iran, because the only thing that links the two countries is that they are oil producers and members of Opec."
Mr Ahmadinejad began his tour in Brazil, where President Luiz Inacio Lula da Silva criticised attempts to isolate Iran over its nuclear ambitions.
But he also urged the Iranian leader to engage with the West.
Western powers fear Iran is developing nuclear weapons technology, rather than civilian uses as it claims.