Can a DUI be expunged in MS?

It can be, but it's not a particularly simple or inexpensive process.

Additional: As above, I believe the CRIMINAL conviction of DUI MAY be able to be expunged, however the DMV record of DUI will always exist. Your DMV record is a cumulative total of ALL your infractions and, especially in the case of DUI's, can be used as an enhancement factor to the sentence if you should commit any further DUI's in the future.