Currently there are no direct flights Sofia to Mongolia.

Flights Sofia to Mongolia with 1 stopover:

Flights via Moscow Sheremetievo (SVO), Moscow, Russia
From Sofia (SOF), Bulgaria with Aeroflot
OR
From Sofia (SOF), Bulgaria with Aerosvit
Transfer at Moscow Sheremetievo (SVO), Moscow, Russia Then on to Buyant Uhaa Airport (ULN), Ulaanbaatar, Mongolia with Aeroflot