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

Return flights

14 Sep - 21 Sep	China Eastern
03 Sep - 11 Sep	China Southern
17 Sep - 20 Sep	China Southern
01 Sep - 04 Sep	China Southern
12 Sep - 18 Sep	China Southern
01 Sep - 20 Sep	China Southern
08 Sep - 16 Sep	China Southern
12 Sep - 20 Sep	China Southern
15 Sep - 20 Sep	China Southern
18 Sep - 29 Sep	China Eastern
15 Sep - 30 Oct	China Southern
24 Sep - 28 Oct	China Southern
24 Sep - 14 Oct	China Southern
25 Sep - 19 Oct	Air China
26 Sep - 14 Oct	China Southern
29 Sep - 14 Oct	China Southern
29 Sep - 18 Oct	China Southern
29 Sep - 16 Oct	China Southern
17 Sep - 04 Oct	China Southern
26 Sep - 15 Oct	ANA

Also check the deals for one-way flights from Seoul to Istanbul 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 Seoul to Istanbul in September from $575

Return flights