The case comes on the back of two separate suicides by army privates last weekend, and a deadly shooting spree last month in which a sergeant killed five members of his unit for taunting him.
The five detained men allegedly assaulted a 23-year-old private in April, striking him in the chest and causing a chunk of food to get lodged in his airway.
The soldier, identified by his surname Yoon, died of asphyxiation.
Investigators said Yoon had been the target of regular bullying, including sessions of crude water-boarding.
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He had also been forced to eat a tube of toothpaste and lick the spit of other soldiers from the ground.
Barrack-room bullying has long tainted South Korea's military service, which is mandatory for all able-bodied men between the ages of 18-35.
Conscripts, most in their early twenties, account for the lion's share of the military's 690,000 active personnel.
Experts say the pressures facing the young servicemen can be daunting when, after what is often quite a cosseted childhood and teenaged youth, they are suddenly plunged into a world of harsh military discipline.