UK aid worth £480,000 was seized by Somalian militants in November 2011.
Humanitarian aid supplies were taken from a warehouse during a raid by al-Shabab, revealed the Department for International Development.
DfID's annual accounts said the £480,000 was written off "following the theft between November 2011 and February 2012, by al-Shabab in southern Somalia, of DfID-funded humanitarian materials and supplies from the offices and warehouses of partner organisations, to which DfID had provided funding to deliver projects and programmes".
The accounts said DfID's partners had "no prior warning of the confiscations being carried out and therefore had no time to prevent the loss by relocating goods".
A DfID spokesperson said: "DfID works in some of the most dangerous places in the world, including Somalia, because tackling the root causes of poverty and instability there ensures a safer world and a safer UK.
"Working in conflict-affected and fragile states carries inherent risk."
He said DfID did all it could "to mitigate against this but, on occasion, losses will occur".
"We work with our partners to design programmes that protect our investment from misuse or theft."