Authorities shut the public zoo in Rio de Janeiro on Thursday until the city improves living conditions for the animals there, environmental officials said.
Visitors turning up to see the monkeys and parrots at the zoo in this year's summer Olympic Games host city found the gates barred.
"It is not in a state to receive visitors," the state environmental institute Ibama said in a statement.
"The Rio zoo is not fulfilling its role of environmental education and is not promoting respect for animals."
The zoo, Brazil's oldest, is home to some 350 species.
It is run by the city hall, which is looking to privatize it.
Ibama said the zoo would be closed temporarily while staff carry out improvements.
"This include giving the animals sufficient food, in enclosures that are clean and environmentally improved."
City environmental authorities were last year fined the equivalent of about $263,000 for the bad state of the zoo, which had been drawing complaints since 2012.
Ibama official Vinicius Modesto de Oliveira told AFP the institute would be fining the city authorities $230 a day until it improves the zoo.
"For several years, Ibama has been asking the city authorities to meet certain requirements for improving conditions for the good of the animals," he said.
"The demands have not been met."
The city hall told AFP in an email that a planned tender for renovating the zoo had been suspended while authorities seek a private company to run the site.
Whoever buys the zoo "will have to invest about 60 million reals ($15.7 million) to implement a two-year project in which the urgent work will be done in a short time," it said.
"The park will receive all the renovation and improvement work needed to meet current norms."