Even so, the memoir, which went on sale in November, holds second place on The New York Times' bestseller list, The Washington Post reported Wednesday.
Palin's first book, "Going Rogue," was released one year ago and became the second-fastest selling political book in history. It went into a second printing three days after its release and went on to sell 2.2 million hardcover copies.
"America by Heart" (subtitled "Reflections on Family, Faith and Flag") had an initial press run of 1 million copies, suggesting its publisher, HarperCollins, didn't expect it to repeat the success of "Rogue," the report said.
HarperCollins said it is pleased with sales of the new book.
"We're happy with how it's selling and expect to see it do well in the holiday season," said Tina Andreadis, a spokeswoman for the imprint, which is owned by Rupert Murdoch's News Corp.
Palin, former governor of Alaska and 2008 Republican vice presidential nominee, is also the star of a travel-reality series called "Sarah Palin's Alaska" and a Fox News commentator.
Duggar sisters unveil Christian dating rules in new book
Handler slams Piers Morgan: 'You're a terrible interviewer'