The pair fell into a crater in the Masaya Volcano
Argentine Rudolf Alvarez, 60, and his guide Adriac Valladares, 25, were studying the Masaya Volcano, south of the capital Managua, when they fell inside its crater.
They had been attached by a rope as they worked close to the edge but fell in when it snapped, the Government said.
A spokesman said: "The rope they used to descend a few metres into the crater of the volcano broke."
They became trapped inside the 400 metre crater and had to be rescued by firemen, using specialist equipment.
Firemen had to use ropes and harnesses to climb down and rescue them.
The Argentine volcanologist and his guide were studying the crater when their rope snapped
The pair were suffering from dehydration due to the high temperatures but are in "good condition and stable", the Government said.
Masaya is one of Nicaragua's most active volcanoes and has been erupting for 6,500 years.
When the Spanish Conquistadors arrived, they found it had erupted into an active lava lake.
It last had a major eruption in 2012.
The volcano last erupted in 2016
The pair were dehydrated when firemen got to them
Nicaragua has 19 volcanoes, including seven active ones, which reach along the west coast of the country.
Surrounded by the Caribbean Plate, an oceanic tectonic place beneath Central America, Nicaragua is home to the majority of the region's Central American Volcanic Arc, a chain of volcanoes spanning from Guatemala to northern Panama.
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It spreads across 930miles, with the highest volcanoes found in Guatemala, including the Tajumulco and Volcán Tacaná which are both over 4,000metres high.
On the other side of the world, India's only volcano has recently woken up after lying dormant for the past 150 years.
Lava and smoke started spewing out of the Barren Island volcano in late January, scientists revealed this week.
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