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

Return flights

15 Sep - 30 Sep	Japan Airlines
15 Sep - 27 Sep	Japan Airlines
15 Sep - 28 Sep	Japan Airlines
15 Sep - 29 Sep	Japan Airlines
15 Sep - 15 Oct	Japan Airlines
17 Sep - 30 Sep	Japan Airlines
16 Sep - 30 Sep	Japan Airlines
15 Sep - 26 Sep	Japan Airlines
29 Sep - 10 Oct	EVA Air
17 Sep - 26 Sep	Japan Airlines
25 Sep - 25 Oct	Japan Airlines
26 Sep - 18 Oct	EVA Air
18 Sep - 25 Sep	ANA
26 Sep - 29 Sep	Alaska Airlines
21 Sep - 05 Oct	ANA
25 Sep - 04 Oct	ANA
22 Sep - 04 Oct	ANA
28 Sep - 19 Oct	Japan Airlines
27 Sep - 10 Oct	STARLUX Airlines
26 Sep - 11 Oct	Japan Airlines

Also check the deals for one-way flights from Seattle to Seoul 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 Seoul in September from $871

Return flights