Venezuelan President Hugo Chavez made the declaration at a Military University ceremony days after his senior defense aide signed agreements with Argentina on integrating the countries' defense industries.
Both countries have ambitions to develop defense industries, vying with Brazil's advanced and sophisticated aerospace and military manufacturing.
It isn't at all clear if either side has a significant existing capacity but, of the two, Argentina has more advanced capacity with a significant footprint in nuclear power generation and related nuclear technologies.
Venezuela was only recently confirmed as a full member of Mercosur after several years of a delay caused by other members' criticism of Chavez's populist style of government and reluctance to ratify the country's membership.
Chavez said Venezuela's defense accords with Argentina would be a step toward "the necessary strategic integration of the armed forces in the framework of Mercosur and turning the bloc into a military power."
There was no immediate Argentine government comment on the declaration by Chavez.
Chavez used the public address to repeat his support for Argentina's claim over Falkland Islands, a British overseas territory.
He said Mercosur was "an important strategic alliance" with an "immense offensive, dissuasive capacity."
Last Friday ministers from Argentina and Venezuela met aboard an Argentine ship in La Guaira and signed a memorandum of understanding on pooling resources for developing their military manufacturing technologies as part of the "necessary strategic integration of the armed forces in the framework of Mercosur."
Chavez said such integration was needed "to help defend our resources, combat colonialism."
However, he said, this had to be done by establishing "a zone of democracy where never again will there be military coups, or invasion or imperialisms, but also a space where only our peoples in their most pure democratic expression and through legitimate governments can decide their future."
Mercosur suspended Paraguay after the Paraguayan Congress voted to impeach Fernando Lugo and remove him from presidency, replacing him with Federico Franco as president. Mercosur called the impeachment and Lugo's ouster a coup, a stance that was supported by the Union of South American States.
Critics of Chavez in several member countries were unwilling to have Venezuela confirmed as full member because they feared his entry will signal a shift toward a populist radicalization of Mercosur.
Venezuela's long-delayed confirmation as full member became possible only after Mercosur suspended Paraguay, whose legislation had been obstructing Venezuela's admission. Even supporters of Venezuela's membership say they would have preferred Venezuela's admission in strict observance of Mercosur's constitution.
The way Venezuela was admitted into Mercosur showed that the general rule of consensus was bypassed, critics say.
Former Brazilian President Fernando Enrique Cardoso told Veja magazine he regarded as serious "the incorporation of Venezuela to Mercosur in the absence of Paraguay. All Mercosur decisions are by consensus, which means the participation of all members."