Amazon.com has reported first-quarter income of $299m, an increase of 68% compared with the same period a year ago.
Net sales increased 46% to $7.13bn topping analysts' estimates of sales of $6.87bn and operating income was up 62% to $394m, compared with the first quarter of 2009.
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Jeff Bezos, founder and chief executive of Amazon.com, emphasised the success of the company's Kindle electronic reader.
"Kindle remains our number-one best-selling product, and earlier this week Kindle selection reached 500,000 titles," he said.
During the quarter, Amazon announced that in addition to English, French and German, authors and publishers can use the self-service Kindle Digital Text Platform to upload and make available their books in Spanish, Portuguese and Italian in the Kindle Store.
But like Microsoft, Amazon's share price fell in after hours trading despite strong results.
About 6% was knocked off the share price because the second quarter forecast of sales worth between $6.1bn and $6.7bn implied a slowdown, according to US reports.
Despite Kindle's good performance, Amazon is going to have to step up its game to counter competition from the newly-released Apple iPad, analysts said.