It follows the search of a house at Sorella Street off the Grosvenor Road in west Belfast yesterday, June 30.
The men were detained under section 41 of the Terrorism Act.
Detective Inspector Stuart Griffin said: “A quantity of suspected ammunition was recovered from the property.
“Both men are currently in custody at Antrim Serious Crime Suite.”
The search operation is believed to relate to ongoing investigation into the activities of ‘violent republican’ groups.
Earlier on Tuesday, a 40-year-old man was arrested and a house searched in the New Lodge.
It was part of what police said was an investigation into dissident republican paramilitary shootings.