PASSPORT & VISA
All visitors to Mongolia require a valid passport with visa unless they come from one of the visa-exempt countries. Visitors from any country planning to stay in Mongolia for more than 30 days must register with the Mongolia Immigration Agency in Ulaanbaatar within the first seven days of arrival. Visitors who fail to register and who stay longer than 30 days, even for reasons beyond their control, will be stopped at departure, temporarily denied exit, and fined.
Click here https://immigration.gov.mn/en/ , http://mongoliavisa.com/