Mongolia Visa Requirements
You will need a visa to enter or transfer through Mongolia. Most visas are valid for a stay of up to 30 days within six months from the date of entry. British citizens can apply for a tourist visa (valid for 30 days) or transit visa (valid for ten days) online.
Passport Validity for Mongolia Travel
Your passport should be valid for a minimum of six months from your date of entry into Mongolia.
For further information, please check with the embassy.