The soldier died as a result of small arms fire near Sangin in Helmand province.
Spokesman for Task Force Helmand, Lieutenant Colonel David Wakefield, said:
"It is my sad duty to inform you that a soldier from 4 RIFLES, serving as part of the 3 RIFLES Battle Group, died this morning near Sangin in northern Helmand province.
"He was on a foot patrol about 700 metres east of Patrol Base Blenheim, to the north east of Sangin district centre.
"The patrol he was on was part of ongoing operations by the 3 RIFLES Battle Group to expand the area of security around the district centre, when he was shot and killed by small arms fire.
"He died doing his duty, boldly confronting the enemy; we will remember him."
Next of kin have been informed and have asked for a period of grace before further details are released.
This death is not connected to Operation MOSHTARAK.