The announcement on Friday by mission officials backs strong indications provided earlier by NASA's Mars Odyssey orbiter in March 2002.
"We have identified water ice on the South Pole," Vittorio Formisano, a European Space Agency scientist said, citing preliminary data gathered by the unmanned spacecraft.
It indicates that the southern polar cap of Mars contains abundant stores of water ice.
The Red Planet's northern ice cap is already thought to contain water ice, along with frozen carbon dioxide, the substance also known as dry ice.
Water, in its liquid form, is one of the ingredients for nurturing and sustaining life, and Mars is considered to be the best bet for this outside Earth.
The confirmation of frozen water is certain to be welcomed by scientists working on de-mystifying the planet.
It comes amid the disconcerting news of NASA losing contact with Spirit, its Mars rover sent to probe the distant planet.
Spirit has stopped communicating with NASA control room since Wednesday.