The Action Against Hunger (Action contre la Faim, or ACF) had in September reduced its number of staff by 60-70 percent and stopped its tsunami relief operations a month after the 17 workers were massacred.
"As the humanitarian situation continues to deteriorate and the population's needs continue to grow, Action contre la Faim decided to resume its activities in the conflict zone," the ACF said in a statement issued in Paris and Colombo.
ACF said it would open a base in Batticaloa, one of the worst affected areas, as fighting continued in the embattled region.
It pledged to provide food and basic needs for at least 14,000 people, as well as supply drinking water and increase hygiene conditions for more than 6,000 displaced people.
The ACF scaled down its operations a week after independent Norwegian truce monitors said Sri Lankan troops killed the 17 aid workers at the northeastern town of Muttur, where security forces had clashed with Tiger rebels.
The Sri Lanka Monitoring Missi