Another seven children were hurt after they fell from the inflatable bouncy castle on January 4 in Mislata on the outskirts of Valencia.
An eight-year-old girl died from her injuries the day after the fairground accident.
“We regret the death of the second girl who was in hospital in serious condition following the accident,” Mislata city hall said in a statement.
The city declared three days of official mourning and cancelled all official events until noon Wednesday in the wake of the girl’s death.
“What terrible sorrow! Despite the extraordinary efforts made by healthcare workers, the second girl injured at the fair has died,” Mislata mayor Carlos Bielsa tweeted.
Police have opened an investigation to determine if the bouncy castle complied with safety rules.
Last month, six children died on Australia’s island state of Tasmania after a gust of wind lifted a large inflatable castle off the ground at an
end-of-term school party.