Abstract: To implement traditional Mongolian operating system is more difficult and more costly. It lies in two issues: (1) Mongolian characters always transform their shapes within different context of text; (2) Mongolian text is written from top to bottom and all columns are arranged from left to right. The first issue involves many characteristics of this script, which make the display of Mongolian textrather complex. The second issue results in special requirements for human-computer interaction, which are not supported by operating systems currently. First, some characteristics of Mongolian script are analyzed. Second, technical details to design a traditional Mongolian operating system are discussed, which include character set and its encoding scheme, transformation of traditional Mongolian characters, text display in a vertical style and graphical user interface special to Mongolian users. Some challenges are discussed and related solutions are presented. Third, an implementation example of operating system to support traditional Mongolian based on Qt/KDE is described in brief. Finally, some work to be done is proposed.