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

Return flights

11 Sep - 13 Sep	Aeromexico
17 Sep - 23 Sep	Volaris
07 Sep - 14 Sep	Volaris
15 Sep - 24 Sep	Volaris
02 Sep - 22 Sep	Volaris
02 Sep - 09 Sep	Volaris
02 Sep - 13 Sep	Volaris
04 Sep - 19 Sep	Alaska Airlines
04 Sep - 10 Sep	Volaris
01 Sep - 30 Sep	Volaris
26 Sep - 07 Oct	Air Canada
26 Sep - 07 Oct	Delta	direct

Also check the deals for one-way flights from Seattle to Mexico City 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 Mexico City in September from $341

Return flights