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

Return flights

16 Sep - 23 Sep	jetBlue
14 Sep - 21 Sep	American Airlines
15 Sep - 21 Sep	American Airlines
09 Sep - 16 Sep	United
15 Sep - 16 Sep	Alaska Airlines
26 Sep - 29 Sep	United
10 Sep - 14 Sep	Alaska Airlines

Also check the deals for one-way flights from Seattle to San Juan 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 San Juan in September from $367

Return flights