The US military court in Afghanistan sentenced the American soldier to six months confinement and a reduction in rank after finding him guilty of punching detainees.
The conviction of Sergeant Kevin Myricks came three days after another soldier was convicted for mistreating the same detainees at a base in eastern Afghanistan in July.
Myricks was found guilty of one count of conspiracy to maltreat a detainee and another count of maltreatment of two detainees. He was reduced in rank to a private and sentenced to six months confinement, a US military statement said.
"The court-martial and subsequent punishment in this case reflects the seriousness with which this command views this incident," Major Geneneral Jason Kamiya, the US-led coalition's operational commander, was cited as saying in a statement.
"Incidents of this nature are not reflective of the standards adhered to by this command. We are fully committed to investigating all allegations of detainee mistreatment and will hold accountable those who are found to have acted inappropriately," he said.
Myricks is being held in custody at the Bagram Airfield, the coalition's headquarters in Afghanistan, awaiting transfer to Kuwait for detention, the statement said.
The allegations of prisoner abuse are not the first to stem from Afghanistan.
In 2002, two Afghans held at Bagram died after being beaten. Fifteen soldiers faced charges for those deaths.
A year later, another Afghan died while being held at a base in southern Helmand province, according to an autopsy report provided by the Defence Department.