The internet retailing giant also said it expected to report a bigger-than-expected loss in the next three-month period.
Amazon shares plunged over 10% in after-hours trading in New York.
Investors have long been wondering when Amazon will turn its significant revenues into profits for shareholders.
Amazon has been spending heavily in various new initiatives, including its Amazon Fresh grocery delivery service in the US, and its $1bn acquisition of video game streaming site Twitch.
That has hurt profits at the firm, with operating expenses growing to $21.1bn, compared with the $17.1bn last year.
Investors have been tolerant of Amazon's policy of reinvesting profits back into the firm. But patience has been wearing thin in recent months.
Shares in the firm have fallen nearly 20% since the beginning of this year.
In a statement accompanying its earnings, Amazon founder and chief executive Jeff Bezos chose instead to focus on the firm's holiday offerings during the crucial period in the run-up to Christmas.
"As we get ready for this upcoming holiday season, we are focused on making the customer experience easier and more stress-free than ever," he said.
Amazon has reported a third-quarter loss of $437m (£273m) - up significantly from the $41m loss it reported for the same period last year.