This article discusses the authors' approach in creating a digital library which can be used to access ancient historical documents written in traditional Mongolian script using a query in modern Mongolian Cyrillic. They introduce a Traditional Mongolian Script Digital Library TMSDL, which aims to preserve over 800 years of historical records written in traditional Mongolian for future use and to make them available for public viewing. The authors present their approaches to solve two major problems for realizing such a digital library; 1 accessing ancient documents using a query in modern Mongolian, and 2 rendering traditional Mongolian script properly. They implement an "ancient-to-modern information retrieval" method, which takes into account historical differences in the writing systems of the ancient and modern Mongolian languages. The authors' results are explored further in the article.