She reportedly died at her Portland home on Monday.
Her last book was the essay collection No Time to Spare: Thinking About What Matters, which came out in 2017.
Over her career she published more than 20 novels, a dozen books of poetry, more than 100 short stories, seven collections of essays, 13 books for children and five volumes of translation including the Tao Te Ching and selected poems by Chilean Nobel Prize victor Gabriela Mistral.
The book was awarded the Nebula and Hugo awards, two of science fiction's highest honors, but Le Guin saw the novel - and all her books that followed - as reaching beyond the genre.
"I eliminated gender to find out what was left", she said of the book.
She married Charles Le Guin in Paris in 1953.
Born Ursula Kroeber in Berkeley, Calif., on October 21, 1929, Le Guin became known for writing stories about sorcery and interplanetary conflict that infused feminist sensibilities and subverted ideas about gender. Some of them are written on my soul.
Novelist Madeline Ashby recounts meeting Le Guin at a lecture, mentioning to Le Guin that she was writing her thesis on her, and Le Guin insisting Ashby send it to her.
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Born Ursula Kroeber in Berkeley, CA, she began writing as a pre-teen, starting first with short stories and moving on to larger works thereafter.
"Throughout her life she embraced new forms of technology; she was constantly pushing boundaries and barriers".
"The Lathe of Heaven" was among the few books by Le Guin that have been adapted for film or television.
Le Guin wrote poetry and short stories, many of them realist in style, before returning to science fiction in the 1960s, inspired in part by the stories of Paul M.A. Linebarger, who wrote under the pseudonym Cordwainer Smith.
"She was one of the first really big voices in science fiction and fantasy who was a woman", Kowal added.
Instead, she populated her novels with richly imagined worlds that drew less from recent science fiction than from ancient mythology or Taoism, the Eastern philosophy that emphasizes acceptance and change.
Many of those writers mourned her death on Tuesday.
Young adult author Garth Nix said he needed to "give thanks for all her deep thought, wisdom and insight, distilled into so many massively influential books and stories". "I miss her as a glorious amusing prickly person, & I miss her as the deepest and smartest of the writers, too".
In 2014, Gaiman presented her withthe National Book Foundation Medal for Distinguished Contribution to American Letters. "And I think a lot of readers hear it, too".