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

Return flights

02 Sep - 17 Sep	Alaska Airlines
17 Sep - 25 Sep	Air Canada
09 Sep - 16 Sep	Air Canada
09 Sep - 15 Oct	Air Canada
18 Sep - 25 Sep	Air Canada
11 Sep - 18 Sep	Air Canada
10 Sep - 22 Sep	Air Canada
08 Sep - 17 Sep	Alaska Airlines
25 Sep - 30 Sep	Air Canada
15 Sep - 30 Sep	Air Canada
10 Sep - 30 Sep	Air Canada
17 Sep - 13 Oct	Air Canada
30 Sep - 28 Oct	Air Canada
24 Sep - 15 Oct	Alaska Airlines
20 Sep - 10 Oct	Air Canada
27 Sep - 05 Oct	Delta	direct
16 Sep - 02 Oct	Delta	direct
09 Sep - 15 Oct	Korean Air	direct
24 Sep - 15 Oct	Delta	direct
17 Sep - 13 Oct	Delta	direct

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 671€

Return flights