Moore, one of the most accomplished performers of her generation, is brilliant as a linguistics professor who starts to lose grip on her memory which has serious implications on her family and job.
"People say that an Oscar award leads to living five years younger and I am happy that I won the award because my husband is younger to me...," an emotional Moore said in her speech.
Moore said people with Alzheimer's often feel isolated but they need to be seen to be cured.
The actress had consolidated her position by winning almost all the trophies -- Golden Globe, Bafta, Critics' Choice awards and Screen Actors Guild Award, in the run up to the Oscars.
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The 54-year-old actress saw off competition from Marion Cotillard (Two Days, One Night), Felicity Jones ('The Theory of Everything'), Rosamund Pike in ('Gone Girl') and Reese Witherspoon in "Wild".
The movie, directed by Richard Glatzer and Wash Westmoreland, is an adaptation of Lisa Genova's best-selling 2007 novel of the same name.
Moore, equally at home in indie movies as well as big budget Hollywood dramas, has made a career out of playing complex roles.
The actress worked as a waitress in New York before finding work as a theatre and TV star.
She made her movie debut in 1990 with "Tales from the Darkside: The Movie" but she was best noticed for her work in Robert Altman's "Short Cut".
Other than her Oscar nominated roles, Moore was praised for her performance in films like "The Big Lebowski", "Magnolia", "Hannibal", "Children of Men", "A Single Man", "The Hunger Games" franchise, "The Kids Are All Right" and "Maps to the Stars".