Most scientists classify the peroid of Mongolian language development from 15-16th century as a modern (new) Mongolian, even the difference between the language and the dialect of that time differs considerably from those of contemporary Mongolian language. For that reason, it is important to improve and encourage the research on peculiarities of Mongolian language in 17th century. From historical monuments of that period we can mention tod letters invented by Zaya bandid Namkhaijamts in 1648, and soyombo, khevtee durvuljin letters designed by Undur Gegeen Zanabazar. Dr. Shagdarsuren mentioned the importance of studying special features of Mongolian language of the 17th century on the basis of errorology and made interesting observations on the original texts of Shar Tuuj .