State television RTS said Broz had died of cardiac arrest.
She was 88 and had lived largely in isolation since the death of Yugoslav leader Josip Broz Tito in 1980, squirreled away in a crumbling state-owned villa in the Serbian capital without a passport or ID.
Born in Croatia, Broz became a nurse with Tito's Partisan fighters in World War Two, then his personal secretary and finally his third wife in 1952.
Tito was 32 years her senior, and presided over a federation of 22 million people balanced between Cold War East and West.
Unlike the grey, staid Communist leaders of the Soviet bloc, Tito and his wife revelled in ostentation and glamour.
Dead three days short of his 88th birthday, Tito's funeral gathered heads of state and dignitaries from across the Cold War divide, including Britain's Margaret Thatcher and ailing Soviet president Leonid Brezhnev.
Life in isolation
Tito's wife had already been removed from the public eye in the late 1970s, as the party elite had grown increasingly suspicious of her influence over the elderly president.
Soon after Tito's funeral, authorities confiscated all property and personal belongings of the couple and placed Broz under virtual house arrest in a dilapidated government-owned villa in Belgrade's hilltop Dedinje district.
With Tito gone and the Cold War over, his widow looked on as nationalist tensions tore apart Yugoslavia in the 1990s, spawning seven new states during a decade of war and ethnic cleansing that killed more than 125,000 people.
Nationalists chipped away at Tito's reputation and legacy, deconstructing the personality cult built around him in an effort to undermine the mantra of 'Brotherhood and Unity' that underpinned Yugoslavia.
His widow was boxed away, out of sight. She lived on a state pension, the villa gradually falling into disrepair.
Then in 2006, responding to a public appeal from Broz's sister, democrats who took power in Serbia with the fall of nationalist strongman Slobodan Milosevic in 2000, undertook to fix the leaking roof and reconnect the heating.
"I remember that it was minus 11 [Celsius] outside and there was no heating in the house," Serbian Trade Minister Rasim Ljajic, who visited Broz in the winter of 2005, said in a recent interview with the Serbian daily Politika.
"It was unbearable," he said. "Jovanka was wearing all her winter clothes."
In 2009, Broz was finally granted a Serbian passport, and though she rarely spoke publicly, she was seen once a year at Tito's mausoleum on the May 4 anniversary of his death.
In one of her last interviews, Broz told the Serbian daily Blic that she absolved Tito of responsibility for her estrangement towards the end of his rule. "Tito loved me until his death," she said.
Blic reported that she had asked to be buried next to Tito.