Traditionally, Mongols practiced Shamanism, worshipping the Blue Sky. However, Tibetan Buddhism gained more popularity after it was introduced in 16th century in 3rd times in Mongolia. In the beginning of the 20th century, Mongolia had hundreds of Buddhist monasteries and temples.
Due to the anti-religious campaign of the communists in the 1930s, which nearly destroyed the majority of monasteries and religious system.
After the democratic revolution in 1990’s, government allowed freedom of religion and over 100 monasteries have reopened, and Kazak Muslims are allowed to practice Islam. Nowadays, around 90% of Mongolians are Buddhist and with some other elements of Christianity, Muslim, and Shamanism.
(Mongolia magazine. MNET, 2016)