Three female lions named Zala, Nima and Run Run, and a male lion named Kiumbe were tested after their keepers noticed they showed slight symptoms of coronavirus.
Zookeepers administered antigen detection tests and all of them tested positive for SARS-CoV-2. The result and diagnosis were confirmed by subsequent PCR tests.
Two staff also tested positive, who are believed to have given the lions the virus.
The Veterinary Service of Barcelona then contacted the Bronx Zoo in New York for advice. Four tigers and three lions at the Bronx Zoo tested positive for COVID-19 in April, in the only other known case where large felines were infected. They all recovered.
"The Zoo has contacted and collaborated with international experts such as the Veterinary Service of the Bronx Zoo, the only one that has documented cases of SARS-CoV-2 infection in felines," the Barcelona zoo said in a statement.
"The lions were given veterinary care for their mild clinical condition — similar to a very mild flu condition — through anti-inflammatory treatment and close monitoring, and the animals responded well."
All symptoms disappeared after 15 days, except for coughing or sneezing, local media reported.
The four-year-old male and the females, who are all 16 years old, had no contact with other animals, the zoo said.
Acting director of the zoo, Juli Mauri, told local media the lions were already recovered.
Mauri told La Vanguardia the lions could not have transmitted the disease to the public as close contact would have been necessary.
Many animals can carry the coronavirus, but few can transmit it to humans. One animal that is cause for concern is the mink, which has transmitted a mutated version of the virus back into humans.