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

Return flights

25 Sep - 28 Sep	Eastar Jet
22 Sep - 28 Sep	Air China
22 Sep - 07 Oct	Air China
24 Sep - 25 Sep	Air China
24 Sep - 03 Oct	Air China
23 Sep - 29 Sep	Air China
26 Sep - 29 Sep	Air China
26 Sep - 28 Sep	Air China
29 Sep - 02 Oct	Air China
28 Sep - 02 Oct	Korean Air
28 Sep - 12 Oct	Air China
28 Sep - 09 Oct	Air China
28 Sep - 01 Oct	Air China
27 Sep - 02 Oct	Air China

Also check the deals for one-way flights from Seoul to Ulaanbaatar 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 Ulaanbaatar in September from $280

Return flights