The military plane crashed in Algeria's mountainous Oum al-Bouaghi province, 450 kilometres from Algiers.
The plane, a Hercules C-130 was heading for the eastern city of Constantine.
Media first reported that 103 people were on board but the Algerian government and military said Wednesday that 78 people were actually on the plane.
Most of the passengers were soldiers or their families.
The only survivor is being treated for serious head injuries.
Bad weather mayn have been the cause of the accident, the defence ministry said in a statement on Tuesday.
Because of wind and snow, signals were distorted and communication with the control tower appears to have been cut
President Abdelaziz Bouteflika has declared three days of mourning.
Search teams were sent on the site to find clues as to the accident's cause in the wreckage.