US passport holders who travel to Mongolia for official, private business and tourism don’t need to obtain a visa for stay up to 90 days.
US citizens need a visa to travel to Mongolia if planning to stay more than 90 days. To stay in Mongolia for more than 90 days or need a multiple entry visas for work / study an Approval from the Office of Immigration, Naturalization and Foreign Citizens in Ulaanbaatar is reuquird. Your sponsor in Mongolia should get you the approval.
NOTE: Other foreign nationals staying in Mongolia for more than 30 days are required to register at local “Office of Immigration, Naturalization and Foreign Citizens“.
Normally visa is processed in 2 working days for US citizens. However, please be advised that the regulations require up to one week for the processing. The same day service (8 work hours for handling) is available for extra fee.