The two men were members of the Royal Logistics Corps and were attached to the 1st Battalion The Royal Welsh Battlegroup. Their families have been informed.
The soldiers were in forward operating base Ouellette, in the northern part of Nahr-e Saraj district, in Helmand province, when it came under "indirect" mortar fire from Taliban fighters on Friday.
Such mortars attacks on army bases in Afghanistan rarely cause injury because the initial explosion from the launch tube warns everybody in the area that a mortar has been fired.
A spokesman for Task Force Helmand, Major Ian Lawrence, said: "Sadly, I must report that today two soldiers from the Royal Logistic Corps, attached to 1st Battalion The Royal Welsh Battlegroup, were killed in an indirect fire attack on their base.
"The thoughts and condolences of everyone serving in the Combined Force are with their families and friends."
A total of 412 members of UK forces have died since operations in Afghanistan began in October 2001.