The attack happened in a chapel at the minimum security area of the prison complex, said spokeswoman Susan Biller.
Biller said the inmate punched the officer in the face, and the officer fell backward and hit his head. The officer was taken to Valley General Hospital where he was treated and released.
The inmate was serving time for a robbery in Grant County, Biller said, and will now be required to have a disciplinary review.
"They'll have to do an investigation based on the infraction and and see what the determination will be with respect to additional time (in jail,)" Biller said.
Biller said they haven't figured out the motive for the attack.
The chapel in Wednesday's attack was a separate location from the chapel where corrections officer Jamie Biendl was killed by inmate Byron Scherf, Biller said. Scherf is now in a Walla Walla after being sentenced to death in the attack.