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

Return flights

30 Sep - 07 Oct	Air Canada
24 Sep - 01 Oct	Air Canada
23 Sep - 30 Sep	Air Canada
29 Sep - 06 Oct	Air Canada
22 Sep - 29 Sep	Air Canada
21 Sep - 29 Sep	Air Canada
28 Sep - 05 Oct	Air Canada
16 Sep - 30 Sep	SWISS
15 Sep - 22 Sep	SWISS
27 Sep - 04 Oct	Air Canada
26 Sep - 03 Oct	Lufthansa
25 Sep - 02 Oct	Austrian Airlines
26 Sep - 05 Oct	Lufthansa
21 Sep - 28 Sep	Lufthansa
16 Sep - 23 Sep	Lufthansa
20 Sep - 27 Sep	Air Canada
17 Sep - 24 Sep	Lufthansa
18 Sep - 25 Sep	Lufthansa
25 Sep - 11 Oct	Iberia
19 Sep - 11 Oct	Air Canada

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 $423

Return flights