Notably, revenue in North American surged 35% year over year to $34.3 billion, while global revenue grew just 13% to $15.5 billion.
Shares of the company fell 5 percent to $1,635 after the bell.
"We are getting more and more creative around getting efficiency up and getting our cost of acquisition down", Amazon's chief financial officer, Brian Olsavsky, told analysts on the company's quarterly earnings call on Thursday.
Sales will be US$56 billion to US$60 billion in the current period, compared with analysts' average estimate of US$61 billion.
Prior to Amazon's earnings release, analysts at SunTrust Robinson Humphrey suggested that the company's own estimates, particularly in the fourth quarter, aren't always impressive.
Amazon's net income rose to US$3.03 billion, or US$6.04 per share, in the quarter ended Dec.31 from US$1.86 billion, or US$3.75 per share, a year earlier, which included a tax gain.
The all-important holiday season fueled 20 percent growth in revenues, to $72.4 billion, while profit grew to $3 billion, up from $1.86 billion a year ago.More news: US Imposes Sanctions On Venezuela's State Oil Giant
Last year, Amazon streamlined its ad products so they were less confusing to brands, and folded them under the Amazon Advertising moniker.
Amazon's widening profits are largely driven by the growth of its high-margin businesses, including its cloud, advertising and third-party seller services. More than 100 million Prime members worldwide pay monthly or yearly fees in exchange for shipping discounts and music and video streaming.
First published January 31, 1: 26 p.m. PT. Update, 2:14 p.m. PT: More details added throughout.
Net income increased to $3.0 billion, or $6.04 per diluted share, compared with net income of $1.9 billion, or $3.75 per diluted share, a year ago and easily topping Street estimates of $5.65 a share.
Amazon was light on specifics but said that 2018 was the biggest holiday shopping season ever for Amazon devices. First-quarter operating income will be US$2.3 billion to US$3.3 billion, in line with analysts' estimates of US$2.99 billion.
Shares of Amazon were moving back and forth in after-hours trading. Its market cap, more than $840bn as of Thursday afternoon, is the largest of any publicly traded company in the world. For the full year, EPS is expected to rise 335% year over year to $19.86 per share, while full-year revenue of $232.37 billion would represent a 30.6% increase year over year. Amazon continues to rapidly ramp-up employment in AWS technology and sales and in its devices business. The online retailer's brick-and-mortar strategy also includes bookstores and a cashierless convenience store called AmazonGo, which lets customers check in with a smartphone app and be charged automatically based on what they remove from the store.