The actor dropped off copies of Maya Angelou`s Mom & Me & Mom, the November pick for her online book club Our Shared Self.
The star left the novels as part of the Books On The Underground movement, which sees "book fairies" leave their favourite reads for people to enjoy.
Watson left about 100 books with some including a hand-written note.
In it, she wrote that she hoped the reader would enjoy the book, and urged them to leave it on the Tube afterwards for others to find.
`Too fabulous`
One Twitter user, @safaf_96, said she felt like Charlie Bucket in Charlie and the Chocolate Factory when she found a book while @siannusmaximus wrote: "The book fairies get a book wizard. Too fabulous for words."
Cordelia Oxley, director of Books on the Underground, said: "We were delighted to have Emma Watson share the latest Our Shared Shelf book club choice, and she even wrote a lovely note to go inside the books. It was Emma`s idea to be a Book Fairy for the day!
"The reaction has been phenomenal. It must be a mixture of how much everyone adores Emma, and how exciting it is to find something as wonderful as a new book on your journey."
Watson, who was appointed UN women goodwill ambassador in July 2014, started her book club earlier this year.
Books on the Underground started in 2012 and leave about 150 books in stations across London each week.
Harry Potter star Emma Watson leaves books on London Underground
03 November 2016
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Harry Potter star Emma Watson has dashed around the London Underground to hide books for passengers.
