Until 31 December 2015 you can visit Mongolia for tourist and business purposes for 30 days without a visa. This is applicable to visits beginning before 31 December and extending into January.
From 1 January 2016 you ’ll need a visa to enter Mongolia. A Mongolian visit visa is usually valid for a stay of up to 30 days within six months from the date of issue. You can extend your visa up to 30 days once within six months. Full details can be found at Immigration of Mongolia.