The soldier, Leandro Jose Luna, was patrolling in Arauca, when his colleague accidentally fired a grenade launcher and the projectile lodged itself in Luna's head.
Taking him by helicopter was too dangerous, so an ambulance transported the soldier to the capital, Bogota, a journey of eight hours.
Doctors in the capital built an improvised operation theater in a car park because of the danger of the grenade exploding. But they managed to remove the weapon.
"Five minutes were decisive," the soldier's surgeon William Sanchez Maldonaldo told reporters. "If the grenade had exploded, there would have been a tragedy."
Meanwhile, the soldier's condition was described as stable, but doctors said he would need several rounds of surgery to get his face back to normal shape.
A grenade is defined as a small missile that contains an explosive or a chemical agent (tear gas, a flame or smoke producer). It can be thrown by hand or fired from a rifle or a launcher.
mg/bk (dpa, EFE)