"The two revolutionary nations and the governments of Iran and Bolivia are natural allies and will boost their relations in the fields of commerce, industry, agriculture, gas, oil and politics," he told Morales on the first day of a two-day trip to Tehran.
"We are striding on a common path towards a brighter future and will remain by each other's side and supportive of one another under any circumstances," Ahmadinejad said, quoted by the state-run television news website.
The website also quoted Morales, whose country sits on South America's second largest gas reserves, as saying he supports Ahmadinejad.
"I support and praise Mr Ahmadinejad's stance against imperialism and defending the rights of the Iranian people," he said. "I also hail Iranian progress in industry and agriculture."
Iran's supreme leader Ayatollah Ali Khamenei also met with Morales and told him that he expected "resistance against arrogant powers" to pay off.
"The awakening of the South American nations who are seeking their rights is an auspicious event which certainly will not make (big) powers happy," Khamenei told Morales, according to the state-run television news website.
"The arrogant powers will put pressure on you since they are against this spirit, but resistance against these pressures and reliance on God will result in victory," Khamenei added.
Morales, who in 2006 became the first indigenous leader of Bolivia, left La Paz on Friday on a trip to Libya and Iran aimed at reinforcing new diplomatic ties made with the two countries.
Energy-rich La Paz and Tehran established relations in September 2007 when Ahmadinejad made an official trip to Bolivia to sign trade and energy accords. Their growing ties have raised concerns in Washington.
In La Paz, Ahmadinejad and Morales signed a joint statement recognising "the rights of developing nations to develop nuclear energy for peaceful purposes."
The United States and its European allies fear that Iran is seeking to build an atomic bomb under the guise of its civilian nuclear programme, a charge that Tehran vehemently denies.
Within Latin America, Bolivia has aligned itself with Venezuela and Cuba, and rejects US influence in the region.
At the time of the La Paz visit, Iran's top Latin America diplomat, Safar Ali Eslamian, denied his country was forming an anti-US bloc with Venezuela and Bolivia, two countries that support Tehran's nuclear programme.
Bolivia opened diplomatic tiew with Libya in August and Morales visited the North African nation on the weekend.
