The operations were suspended after the abduction of a Russian aid official, Nina Davydovich.
Ms Davydovich, the head of Russian non-governmental organisation Druzhba (Friendship), disappeared on 29 July and has not been seen since.
Russian authorities blamed the abduction on Chechen rebels, although no-one has admitted responsibility.
A spokeswoman for the UN Office for Co-ordination of Humanitarian Affairs, Viktoria Zotikova, said the resumption of operations had been prompted by the growing needs of Chechen civilians.
"Talking with people in the North Caucasus, we saw that the needs now are so great that we must resume work," she said.
Release call
The United Nations nevertheless stressed it remained very worried about the risky situation in war-torn Chechnya.
Two weeks after Ms Davydovich's disappearance, Arjan Erkel, a Dutch national working for medical aid organisation Medecins Sans Frontieres (MSF), was kidnapped in the neighbouring Russian Republic of Dagestan.
Ms Zotikova said UN officials had held consultations with the Russian Government on security issues and had re-evaluated and improved their own security efforts.
She said the United Nations was reiterating its call for the immediate release of Ms Davidovich and MSF's Arjan Erkel.
During the suspension of its operations, the UN continued nonetheless to supply clean water to the Chechen capital, Grozny.
Food aid, health care and education programmes were disrupted.
In July alone, 130,000 people in Chechnya received provisions from the UN World Food Programme, which worked there in collaboration with non-governmental organisations.