"The two countries have a common position in relation to peaceful nuclear activities and insist (on defending their) rights," he told a conference in Tehran, according to the Brazilian daily Folha de S. Paulo.
The nuclear issue has become the major sticking point in relations between Iran and the West.
The United States and Europe suspect Iran is trying to build nuclear weapons. A UN-sponsored deal on having some of Iran's uranium enriched outside of the country is currently being negotiated.
Amid that wrangling, Iranian President Mahmoud Ahmadinejad is preparing to visit Brazil on November 23. His Brazilian counterpart and host, Luiz Inacio Lula da Silva, has defended Iran's right to a civilian nuclear program.
Mottaki elaborated on that, saying the joint position of Iran and Brazil was "peaceful nuclear energy for everyone, and nuclear weapons for no one."
Ahmadinejad and Lula last met in September, on the sidelines of a UN General Assembly gathering in New York.
UN Security Council members Britain, China, France, Russia and the United States, plus Germany, have been working to convince a reluctant Tehran to suspend its uranium enrichment efforts in exchange for trade and political benefits.
Iran has said it will accept the principle of a deal calling for it to send hundreds of kilograms of low-enriched uranium to Russia for further refining.
But one of its state-owned television stations said it was holding out for important, unspecified changes to the arrangement.