The nest housing 96 eggs is located in the Khao Lampi-Hat Thai Muang National Park.
Of the 96 eggs, 48 hatchlings made it to the sea on Monday night, while 12 eggs did not hatch and 36 eggs were not fertilised.
National park officials believe the eggs did not hatch because the nest was too deep — 72 centimetres into the ground.
The officials also said the eggs hatched six days later than the usual 55 days.
The unhatched and unfertilised eggs have been sent to the Phuket Marine Biological Centre for research.
On March 25, 42 leatherback sea turtle hatchlings from another nest housing 79 eggs had made it to the sea. However, three hatchlings died and 34 eggs were not fertilised.
National park officials believe the three hatchlings died because they were not able to climb out of their nest, which was about a metre deep into the ground.