The old zoo was established in 1903 as part of the project landscape architect Carlos Thays, who was also commissioned the design of the then West Park (now known as Parque General San Martin).

He devised an ambitious project to place it on the northeast slope of Cerro de la Gloria.

Taking inspiration from various zoos around the world, the architect designed semi open enclosures that simulate natural habitats and enough space for animals, without bars or cages, just with different levels and building stone walls of the curvature of the hill.

The zoo was officially opened in 1941, covering 40 hectares (99 acres) and including 6.5 kilometres (4.0 mi) of paths and roads.

Since this was the first time an animal was granted this status, it caught the attention of biologist, philosopher, politicians and judges worldwide.