*On top of rotting in prison in Nevada on a robbery conviction, former football great and actor O. J. Simpson is on the hook for $300,000 in back taxes to the state of California, reports TMZ.

According to docs recently filed by the State of CA Franchise Tax Board, specifically Simpson still owes $318,566.04 in unpaid taxes from the year 2000.

The bottom line is that O.J. is in deep, deep financial trouble … he has a federal lien filed against him for the years 2007-2010, for $179,435.07.

Not to mention he still owes MILLIONS to the families of Nicole Brown Simpson and Ronald Goldman … for causing their death.