Tens of thousands of Tigrayans have been displaced during seven months of conflict between regional forces and the Ethiopian army.
MSF said a third of children screened in rural clinics are malnourished adding that aid was rarely extended beyond large towns.
Reports say some families are eating just once a day, and often only bread.
The charity said the situation would probably worsen during the approaching rainy season as the war is preventing farmers from going to their fields.
