For more than 400,000 titles, hardcovers are at least 30 percent off and every paperback is at least 20 percent off. Specially featured books are discounted 40 percent.
In trading today, Amazon's stock fell 1-1/4 to 19. Its original offering price was $18, although the stock has traded as high as $30.
Analysts say today's price cuts reflects growing competition in the Internet bookseller's market, not financial problems at the online store. Amazon.com's IPO has been watched closely as a barometer of market interest in Internet start-ups and e-commerce.
Nicole Vanderbildt, who follows the industry for Jupiter Communications, said the cuts seemed aimed at matching recent reductions by Barnes & Noble's online bookstore. But she added: "I find it hard to believe that [Amazon.com] is not doing well."
A spokeswoman for Amazon.com would not comment whether the company was meeting, falling short of, or exceeding its sales expectations since last month's IPO. She said the company's top executives were also not available for comment.
In a statement, Amazon.com chief executive Jeff Bezos said: "We've always offered the biggest selection, and with these prices, Amazon.com offers the lowest everyday book prices anywhere in the world, online or off."
In related news today, Amazon.com announced a new feature, dubbed "the Partner," which can recommend books to customers that have similar tastes in books. It finds the three most popular titles bought by other readers of the Partner.