The former general, who seized power in the northwest African nation in an August 2008 coup, campaigned strongly on his success in fighting armed groups linked to Al-Qaeda at home and in neighbouring Sahel nations.
Preliminary results released by the Independent National Electoral Commission (INEC) indicated that Abdel Aziz was firmly ahead of anti-slavery candidate Biram Ould Dah Ould Abeid, who obtained 8.67 per cent of Saturday's ballot.
One 70-year-old voter who gave his name only as Brahim said the country, wracked by jihadist violence up until 2010, "had found peace".
"That's important and I want it to continue because peace is irreplaceable."
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Kidnappings and attacks by Al-Qaeda in the Islamic Maghreb (AQIM) were frequent when Abdel Aziz came to power, but he boasts that he has turned his nation into a regional haven of peace thanks to his reorganisation of the military and security forces.
In 2010 and 2011, Mauritanian troops carried out successful "preventative" raids on AQIM bases in neighbouring Mali, before the armed fundamentalists could carry out planned attacks on Mauritania.
But while many voters expressed support for Abdel Aziz's gains against militants, even his supporters were not content with security alone.
The president "has achieved a lot for Mauritania, but we ask him for more", said Ould Bahaya Ikebra, a civil servant.
"We call on him to fight against unemployment, increase wages and lower prices," he said.
Main opposition parties have never accepted Abdel Aziz's 2009 victory in an election they said was marred by massive fraud.