Los Angeles and New York are the first cities to benefit from this new service, which was born from a new deal between the online retail giant and the Postal Service.
The Sunday service may expand to Dallas, Houston, New Orleans and Phoenix sometime next year.
Amazon is not charging extra for the new service.
The company hopes that adding Sunday as a delivery option will generate more sales. It expects the service will be popular with customers with Prime memberships, which costs $79 a year and comes with free two-day shipping on many items as well as access to Amazon's TV and movie streaming service.
"For Prime members, it's free, for non-Prime members, it's like any other delivery day of the week," said Dave Clark, vice president of worldwide operations and customer service at Amazon.
Amazon has considered Sunday delivery for a long time. The company does not disclose the percentage of its packages that are delivered on weekends, but Clark expects customers "to be delighted that they will get their products on a weekend."
Financial terms of the arrangement were not disclosed, but the deal will likely to give the financially ailing Postal Service a boost. The agency, which lost $16 billion last year, had tried but failed to end Saturday mail delivery as a cost-saving measure.
Shares of Amazon.com Inc. climbed $1.69 to $52 in morning trading.
The Associated Press contributed to this report.
