AirHint found the following cheapest return flights from Seattle (SEA) to Barcelona (BCN) in September 2025 (see full year).

Return flights

10 Sep - 23 Sep	Scandinavian Airlines
21 Sep - 30 Sep	Scandinavian Airlines
11 Sep - 17 Sep	Icelandair
18 Sep - 24 Sep	Air Canada
10 Sep - 17 Sep	Icelandair
21 Sep - 29 Sep	Air Canada
01 Sep - 14 Sep	Icelandair
22 Sep - 29 Sep	United
09 Sep - 16 Sep	United
03 Sep - 10 Sep	United

Also check the deals for one-way flights from Seattle to Barcelona in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Seattle to Barcelona in September from $513

Return flights