There are 4 aviation companies in Mongolia, 3 of them are private having domestic flights between Ulaanbaatar, the capital city of Mongolia to other major cities such as Ulgii, Khovd, Ulaangom, Uliastay, Altay, Dalanzadgad, Murun, Oyu Tolgoi etc. Other company which is state owned company and is called MIAT . Mongolian Airlines. MIAT only does international flights between Ulaanbaatar, Beijing, Ulaanbaatar Frankfurt, Ulaanbaatar Hong Kong, Ulaanbaatar Seoul, Ulaanbaatar Tokyo, Ulaanbaatar Moscow. Other 3 private companies are called, Hunnu airlines, Aeromongolia and EZNIS airways. Nowadays these private companies started doing international flight too. Aeromongolia does flights between Ulaanbaatar and Chinese Hohhot, Ulaanbaatar to Irkutsk of Russia. Hunnu Airlines does Flights between Ulaanbaatar and Bishkek, Ulaanbaatar to Nursultan and Almaty.
Domestic flights in Mongolia are only between Ulaanbaatar and other towns, there are no flights in Mongolia between other towns. If you want to fly from Ulgii to Murun for instance, you will have to fly from Ulgii back to Ulaanbaatar then fly to Murun from there. Flying in Mongolia is considered to be pretty safe due. These companies own Fokker 50, Fokker 100 and smaller Airbuses. Domestic flight tickets cost between 250 to 300 USD per person round way tickets between Ulaanbaatar and other towns. Prices are almost the same. However, during the festival season such as Naadam and Eagle Festival etc, domestic ticket prices go up to double due to high demand. Domestic flights in Mongolia are not 100% reliable , aviation companies easily change the schedule of their flights with no proper reason and explanation, they may just say Sorry. This happens Sometimes due to winds and storms but mostly other reasons such as renting their planes to big mining companies at their last minute request. So Our recommendation is that it is always best to have your travel agency book your tickets rather than you book online by yourself as you may not be reimbursed in such case and booking through a travel agency will give you a chance not to miss your flight or to adjust your other plannings accordingly.