Her son, Theo Downes-Le Guin, said the cause was not immediately known.
Her last book was the essay collection No Time to Spare: Thinking About What Matters, which came out in 2017. Le Guin, renowned author of The Earthsea Cycle series and literally scores of other works like The Left Hand Of Darkness, has shuffled off this mortal coil.
Still, Le Guin's fantastical writing style made her something of a literary outsider - a role that she embraced in later years, decrying profit-minded publishers who market writers "like deodorant, and tell us what to publish, what to write".
Her work was also marked by loving descriptions of the natural world, and by her ability to give dramatic shape to complex political ideas - she won the Hugo and Nebula again for The Dispossessed, a long utopian novel that contrasts the capitalist planet of Urras with the anarchist world of Anarres.
She married Charles Le Guin in Paris in 1953.More news: Halep hammers Pliskova for final four spot
More news: Jamaica declares emergency in Montego Bay
More news: 'Cold War Mentality': US Defense Strategy Includes False Judgments on China
A member of the Class of 1947 of Berkeley High School, Le Guin was the daughter of anthropologists, Alfred L. Kroeber and Theodora Quinn Kroeber.
It is with a heavy heart and a saddened soul that I write this tonight.
Fantasy author Garth Nix wrote, "I just saw the sad news that Ursula K. Le Guin has died". Across more than 20 novels and scores of short stories, Le Guin crafted fantastic worlds to grapple with profoundly hard questions here on Earth, from class divisions to feminist theory.
"It probably hurts the sales of my realistic books like Searoad because it tends to get stuck into science fiction, where browsing readers that didn't read science fiction would never see it". But in early adolescence she lost interest in science fiction, because, she recalled, the stories "seemed to be all about hardware and soldiers: White men go forth and conquer the universe". In 2000, the U.S. Library of Congress named her a Living Legend for her contribution to American literature.
Le Guin was a self-proclaimed Taoist who sought balance and harmony in all things. "Not just a science fiction writer; a literary icon". "We'll need writers who can remember freedom - poets, visionaries - realists of a larger reality". There are dozens more awards that she earned, but suffice to say that she was beloved and respected by her peers and fans.
"I know that I am always called 'the sci-fi writer.' Everybody wants to stick me into that one box, while I really live in several boxes", she told reviewer Mark Wilson of Scifi.com.She then turned to genre. "I miss her as a glorious amusing prickly person, & I miss her as the deepest and smartest of the writers, too". "I'll be re-reading her for the rest of my life".