On the Dissimilatory Weakening ofThis article focuses on a kind of sound change of some initial consonants in Mongolian language. In the authors point of view, the sound change is a kind of dissimilatory weakening that some initial consonants (t-, ?-, q-/k-, ?-(si), s-, p-) in written Mongolian change into corresponding weak segments (d, ?, ?, j, dz, b) in some Mongolian dialects. On the basis of examples collected from the Chakhar dialect, reasons, rules and complications of the dissimilatory weakening are probed into. At the same time, related issues such as distribution and chronology of the phenomenon are also discussed.