The companies failed to reach an agreement regarding the terms of a contract renewal, and the current partnership is scheduled to end on March 31, 2016.
The current deal dates back 16 years.
“We were unable to reach terms that would have made economic sense for our company and shareholders,” American Express CEO Kenneth Chenault announced in a statement.
On Thursday, February 12, shares of both companies rose, while shares of American Express fell $5.06 to $80.95.
According to the National Retail Federation, Costco is currently the second largest retailer by revenue in the world.
The company has 474 locations in the United States and 88 in Canada, where a similar deal with AmEx ended last year.
The wholesale retailer also has a number of locations in the UK, Australia, Mexico, Taiwan, Japan, and South Korea.