Winfrey posted a picture on Instagram of herself and her mother at a family gathering.
Lee, who was 83, died in her Milwaukee home, the family told multiple media outlets in a statement. No other details were provided.
Vernita Lee was a teenager when she gave birth to Winfrey in 1954. She then moved to Milwaukee to live with her mother.
Oprah and her mother had a strained relationship that the talk show megastar openly discussed her hard past with Lee.
Vernita is survived by Oprah, her other daughter Patricia, as well as numerous grand children and great grand children.
A private funeral has already been held, with memorial donations being made to Feeding America.
Oprah's one remaining sibling, Patricia, was put up for adoption when she was born but reconnected with her biological family later in life.
China welcomes defeat of Taiwan's ruling DPP in local elections
Chiang Kai-shek's Nationalists rebased their government to Taiwan in 1949 amid the civil war with Mao Zedong's Communists. The DPP lost control of a number of the party's previous strongholds, including the southern city of Kaohsiung.
"[Oprah's] mother wrote me", Winfrey's father, Vernon Winfrey, told PEOPLE previously, "and told me that, you know, the baby had just come, in a letter: what it weighed, what its name was and so forth and so on". The media mogul was raised by her grandmother before being sent to live with Lee at six years old, which she discussed in a 2015 interview with OWN.
"I suddenly land in a place that's completely foreign to me".
Lee is survived by her daughters as well as four grandchildren and four great-grandchildren.
"I was asking the question".
She added: "I lost my attractive grandma on Thanksgiving".