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

Return flights

21 Sep - 16 Oct	Asiana Airlines
09 Sep - 18 Sep	Asiana Airlines
09 Sep - 23 Sep	Asiana Airlines
07 Sep - 23 Sep	Asiana Airlines
09 Sep - 16 Sep	Asiana Airlines
08 Sep - 17 Sep	Asiana Airlines
07 Sep - 18 Sep	Asiana Airlines
07 Sep - 21 Sep	Asiana Airlines
08 Sep - 15 Sep	Asiana Airlines
22 Sep - 26 Sep	Asiana Airlines
24 Sep - 27 Oct	Asiana Airlines
13 Sep - 27 Sep	Asiana Airlines
26 Sep - 03 Oct	Asiana Airlines
30 Sep - 09 Oct	Korean Air
27 Sep - 31 Oct	Asiana Airlines
27 Sep - 11 Oct	Asiana Airlines

Also check the deals for one-way flights from Seattle to Bangkok 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 Bangkok in September from $635

Return flights