Sergeant Javal Davis on Tuesday admitted to stomping on the fingers and toes of a group of seven bound and hooded prisoners in November 2003.
Other guards then undressed the prisoners and stacked them into a naked human pyramid.
In a separate case heard at the same base in Texas, military intelligence soldier Specialist Roman Krol pleaded guilty to pouring water on prisoners as they crawled naked on the floor and throwing a football at them.
The military judge sentenced him to 10 months in prison, reduced his rank to private and gave him a bad conduct discharge.
Davis is from the US army's 372nd Military Police Company - the unit from which seven reservists have been charged with abuses. They include Private First Class Lynndie England, who was pictured holding a leash tethered to a naked prisoner.
Davis argues he and other guards roughed up prisoners at the behest of intelligence officials who wanted to extract information from the prisoners.
"Basically, when the intelligence personnel, when they bring them down there, anyone that comes in there with intelligence value, they want to interrogate them and they would ask you to loosen them up," he said.
Davis admitted his guilt on three charges - dereliction of duty, making a false official statement and battery.
The court will choose a military jury on Wednesday to decide the punishment.
A US military court has already sentenced Charles Graner, the alleged ringleader in the abuse of prisoners at Abu Ghraib, to 10 years in prison.