The guards were on duty in the unit where Castro was being held the night he hanged himself.
Caleb Ackley and Ryan Murphy, the guards were both hired at the Correctional Reception Center in Orient, Ohio in 2007.
The two are on paid administrative leave pending the outcome of an investigation by the Ohio State Highway Patrol and the Department of Corrections.
Castro was found hanged with a bedsheet in his cell on September 3. Prison staff tried to revive him, but were unsuccessful.
Castro pleaded guilty last month to 937 counts, including the kidnappings of Georgina DeJesus, Amanda Berry and Michelle Knight. He was sentenced to life plus 1,000 years.