American Express attributed the performance to currency exchange rates as well as spending to attract new customers as its partnership with retailer Costco ends next year.
"Against the backdrop of a challenging environment and an uneven global economy, we continued to move forward with initiatives to build our business for the years ahead," said CEO Kenneth Chenault in a statement.
Diluted earnings per share fell 11 percent from $1.40 in the previous year. Total revenue, meanwhile, slid 1 percent from $8.3 billion.
Consolidated expenses rose 3 percent from last year to $5.7 billion, driven by increased marketing efforts and investment in technology.
"The marketing and rewards spend is a big part of this story. They're not growing as fast as some of their peers," Tim Seymour of Triogem Asset Management said Wednesday on CNBC's "Closing Bell."
American Express said it expects full-year earnings to be between $5.20 and $5.35 per share after saying previously they would be "flat to modestly down" from the previous year. It reaffirmed previous expectations that it would have positive earnings growth in 2016.
Wal-Mart unit Sam's Club started accepting American Express cards at the beginning of the month. It follows the announcement earlier this year that American Express and Costco would end their exclusive relationship.
American Express shares have plunged about 17 percent this year.