An extended product offering and the introduction of the Kindle book reader saw shoppers flocking to the site over the Christmas period.
Amazon reported a net profit of $384m (£238m), up from $225m in the same quarter a year ago.
Sales rose 42 per cent to $9.5bn, helped by favourable changes in foreign exchange rates, the firm said.
For 2009 as a whole, Amazon's profit rose 40 per cent to $902m.
Looking ahead, the firm said it expects sales in the first three months of the year to grow between 32 and 43 per cent compared with the first quarter of 2009.