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

Return flights

13 Sep - 19 Sep	Air China
10 Sep - 13 Sep	Air China
01 Sep - 03 Sep	Air China
04 Sep - 09 Sep	Air China
06 Sep - 09 Sep	Air China
07 Sep - 10 Sep	Air China
09 Sep - 15 Sep	Air China
11 Sep - 15 Sep	Air China
15 Sep - 19 Sep	Air China
15 Sep - 22 Sep	Air China
26 Sep - 01 Oct	Air China
28 Sep - 05 Oct	Korean Air
29 Sep - 05 Oct	Air China
27 Sep - 04 Oct	Air China
30 Sep - 07 Oct	Air China
27 Sep - 08 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 $384

Return flights