His previous victory was rejected by the incumbent, Laurent Gbagbo, sparking a civil war which killed 3,000 people.
Mr Ouattara's closest challenger, Pascal Affi N'Guessan, got 9%. He is an ally of Mr Gbagbo who faces trial at the International Criminal Court.
Several candidates withdrew from the poll, saying it was not free and fair.
However, on Monday US election observers said the election was credible.
Mr Ouattara required more than 50% of the vote to avoid a run-off.
The 55% turnout was sharply down compared to 80% in 2010.
The last elections sparked five months of violence when Mr Gbagbo refused to step down.
He is now in The Hague, where his trial on war crimes charges, which he denies, has been put back to 28 January 2016.
After two civil wars, most of the country will simply be happy these elections passed by peacefully.
Relatively low voter turnout may concern the president but he clearly has support from all corners of the country as he won in 30 out of 31 regions.
His strongest support lies in the north, where he won close to 100% of the vote in some areas.
The scale of that victory may raise some eyebrows.
But those opposed to Mr Ouattara may simply have decided not to vote after three candidates dropped out of the race.
They cited a lack of transparency, a claim that was not backed up by a heavy presence of election observers who declared the elections free and fair.
While President Ouattara has been praised for transforming the economy and returning Ivory Coast to the economic success story it was in the 1970s, he has also been criticised for not doing enough for reconciliation and justice.
When I interviewed Mr Ouattara before the elections, he said these issues would be his priorities if wins a second term.
Ivory Coast's President Alassane Ouattara has won a second five-year term with nearly 84% of the vote, electoral commission officials say.