Gbagbo, 65, had been charged with undermining state security, BBC reports said. Her husband, former Ivorian President Laurent Gbagbo, is awaiting trial at the International Criminal Court.
More than 3,000 people died in the violence that followed the 2010 presidential poll after the ex-leader refused to accept defeat to Alassane Ouattara.
And it was in the same city where Gbagbo - once called the "Iron Lady" - faced trial. She was also accused of disturbing public order and organising armed gangs. She and her husband were arrested in 2011 after troops stormed a bunker where the pair had taken refuge in the main city, Abidjan.
The court unanimously sentenced her to 20 years, twice as long as the prosecutors had asked for.
Simone Gbagbo's lawyer said they would appeal.
Laurent Gbagbo, is facing four charges at the ICC in The Hague, including murder, rape and persecution.
The ICC had issued an arrest warrant for Simone Gbagbo too, but this was dismissed by the Ivorian government.