Ed Del Pozo, the airline’s El Salvador country manager, said he was "delighted" that American would be offering a second daily flight during this year’s summer season.
"This additional service from Miami complements our existing service to San Salvador from Los Angeles and offers passengers flying through our Miami hub a host of additional convenient connections to other U.S cities, Europe, the Caribbean and South America," he said.
A 148-seat Boeing 737-800 will be used on the flight, an aircraft that features 16 business class seats and 132 economy class seats.
American Airlines, along with its regional subsidiary American Eagle, currently fly to 42 destinations in Latin America and Mexico.
Earlier this month the airline was named among the top 50 employers in the US by readers of Equal Opportunity magazine.