Zeituni Onyango died in her sleep in the US city of Boston on Monday night, after falling ill in January, Margaret Wong said yesterday.
"The United States Kenyan community mourns the loss of Zeituni Onyango, known to her friends as 'Auntie,' and half-aunt of President Barack Obama," Wong said in a statement.
Onyango was granted asylum in May 2010 after going to court to fight a 2004 deportation order, testifying that she faced "tribal violence" in her homeland.
She was unearthed by the media in 2008, days before Obama won his historic election as the first African-American president.
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Wong said Onyango was born under a mango tree in Kenya, where she raised a family and worked in the computer department at Kenya Breweries.
She was step-sister to Obama's late father, a Kenyan who married a white American. She gave birth to the future president in Hawaii.
Onyango moved to the United States in 2000 and applied for political asylum two years later, but was turned down. She was ordered deported in 2004.
Wong had said Obama did not submit written support for Onyango's asylum. The aunt said she had severed ties to the president after her troubles became public.
In 2012 she published her memoirs, "Tears of Abuse."
Of her family she wrote, "The Obama Clan is like the Baobab tree; the strength lies in its roots. The conviction to produce results is cherished.