Dr Narong Sahamethapat, Permanent Secretary, said the declaration was signed today and would take effect one day after it was published in the Royal Gazette.
Ebola is thus included in Thailand's list of hazardous infectious diseases in addition to cholera, smallpox, yellow fever, plague, and severe acute respiratory syndrome (SARS).
The Ministry of Public Health also declares Guinea, Sierra Leone, Liberia and Lagos, Nigeria as EVD contagious areas.
The declaration was intended to warn people, but travel to the areas has not been banned, Dr Narong said.
In the past 79 days, 483 people arrived in Thailand from the countries having the Ebola outbreak and all of them remain healthy, Dr Narong said.
The World Health Organization reported 1,848 EVD patients overall with a death toll of 1,013.
The fatality rate of the disease dropped to 60 per cent due to experienced medical personnel and more precautions being taken.