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

Return flights

26 Aug - 12 Sep	T'way Air
27 Aug - 08 Sep	T'way Air
30 Aug - 08 Sep	Korean Air
31 Aug - 08 Sep	T'way Air
24 Aug - 28 Aug	Eastar Jet
25 Aug - 29 Aug	Air Busan
08 Aug - 12 Aug	Jin Air
15 Aug - 05 Sep	Air Busan
25 Aug - 08 Sep	T'way Air
23 Aug - 01 Sep	Korean Air
23 Aug - 02 Sep	Korean Air
01 Aug - 08 Aug	Air China
06 Aug - 14 Aug	Air China
28 Aug - 07 Sep	Air China
03 Aug - 10 Aug	Air China
23 Aug - 29 Aug	Air China
22 Aug - 30 Aug	Air China
14 Aug - 18 Aug	Air China
26 Aug - 01 Sep	Air China
09 Aug - 12 Aug	Air China

Also check the deals for one-way flights from Seoul to Ulaanbaatar in August.

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 August from $369

Return flights