Mr Chavez and fellow leftist President Evo Morales, of Bolivia, both support Iran's controversial nuclear program and, like Mr Ahmadinejad, are virulent critics of the US administration.
The two South American nations have reached a number of trade and aid agreements with Iran, particularly in the energy sector.
In La Paz, Mr Ahmadinejad and Mr Morales signed a joint statement recognizing "the rights of developing nations to develop nuclear energy for peaceful purposes."
Iran rejects US charges that it is trying to build atomic weapons under the guise of its civilian nuclear program and insists it is entitled to pursue uranium enrichment as a signatory to the Non-Proliferation Treaty.
Mr Ahmadinejad and Mr Morales also signed a number of bilateral agreements, including 100 million dollars in Iranian financing for projects in the South American country.
Relations with Bolivia
Mr Morales' meeting with Mr Ahmadinejad had raised eyebrows in Washington, and the US ambassador in La Paz expressed concerns over Bolivia's warming relations with Iran.
It also drew objections from Bolivian politicians.
"It is of concern that a head of state questioned for his nuclear activities and support of terrorism should come on a state visit," says former Bolivian president Jorge Quiroga.
"Iran represents the greatest threat of nuclear proliferation on the planet."
Bolivia, one of Latin America's poorest countries, recently re-established diplomatic ties with Iran, a country that is under UN-imposed sanctions for its refusal to heed ultimatums to suspend uranium enrichment.
Earlier this week, Mr Chavez poked fun at critics of his strong ties with Mr Ahmadinejad.
"They will say I am plotting with Iran to threaten the world, that we will build an atomic bomb," he says in a weekly televised address on Sunday.
Mr Chavez insisted Mr Ahmadinejad is a man "who respects international peace."
"The president, my friend Ahmadinejad, is an extraordinary human being, who believes in God and is very humble," the Venezuelan leader says.
It is the Iranian leader's third trip to Venezuela since he took office in 2005.
The Iranian leader's mini-tour of South America follows his visit to New York, where he addressed the UN General Assembly and delivered a speech at Columbia University.