Generally, everyone entering Mongolia must have a visa to stay for 30. All types of visas can be obtained from Mongolian Embassies, Consulates, and Honorary Consulates, and other missions abroad. It is also possible to obtain a 30-day tourist or 7-day transit visa at entry points into the country, including Chinggis Khan Airport, Zamiin Uud, and Sukhbaatar aimag railway points.
For all types of visa applications, you will need the following. In order to stay for longer than 30 days, you must get a letter from a tourist agency, a Mongolian citizen, or a resident expat.  Look Mongolian offers visa support for a fee of about $30.

• Your passport with at least one blank page.
• The passport must be valid for 6 months from your time of entry.
• Two copies of recent passport-size photos

Visa Fee: Mongolia visas generally cost around US$ 25 and a transit visa costs US$ 15. If you require the visa urgently or if you obtain the visa at a border point, you will need to pay US$ 50 or US$ respectively. To apply for a tourist visa, a letter of invitation from a hosting organization is required. Many tourist agencies, as well as hosts, are happy to provide this letter.
Please remember that you will need to check the visa requirements for the gateway countries into Mongolia: China, Russia, Korea, etc. In some cases, you will need two visas, one for Mongolia and one for the country you are passing through or a double entry visa for the stops you make prior to arriving in Mongolia and after departing.
Remember that a visa will take about a week to process. An urgent visa will cost you more, but can usually be delivered in much less than a week.

REGISTRATION
If you plan to stay for longer than 30 days, you must register at the Office of Immigration, Naturalization, and Foreign Citizens. This must be done in your first 30 days for most people, or within your first week if you are a US citizen.
Please click the link for a list of NATIONALS OF FOLLOWING COUNTRIES ARE EXEMPTED FROM VISA TO ENTER MONGOLIA
(as June 2019)