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

Return flights

08 Sep - 15 Sep	China Eastern
14 Sep - 21 Sep	ANA
05 Sep - 21 Sep	ANA
26 Sep - 11 Oct	ANA
28 Sep - 19 Oct	ANA
09 Sep - 16 Sep	ANA
08 Sep - 25 Sep	ANA
23 Sep - 29 Sep	ANA
11 Sep - 17 Sep	ANA
01 Sep - 09 Sep	ANA
24 Sep - 15 Oct	ANA
24 Sep - 30 Sep	ANA
29 Sep - 20 Oct	ANA
30 Sep - 07 Oct	ANA

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 $961

Return flights