The Khao Kheow Open Zoo was established in 1974 with area of about 200 acres in Khao Yai National Park due to the increasing number of animals in the Dusit Zoo. In 1978, the zoo was opened to the public. In 1984, zoological park organisation allowed on expansion the area to about 1000 acres for wildlife conservation in the Khao Yai Mountain area. Princess Sirindhorn also gave tremendous support to rescue injured animals and wildlife in this project. Subsequently, the Thai government decided to expand the area about 800 acres more to support education and research about the environment.