Police were called in to shoot the lion to "ensure the safety of tourists", after the feline fatally injured a keeper who entered its cage for cleaning, according to the official Xinhua news agency.
The lion escaped from its enclosure and was at large in the zoo for about two hours, reports said.
Zoos and animal parks have proliferated in China over the last few decades, as an economic boom has stimulated domestic tourism.
Police are still probing the death, which occurred in Taian, in the eastern province of Shandong, yesterday, Xinhua said.
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In that case, reports at the time said the animal was tranquillised.
Two keepers at a zoo in Shanghai were killed by tigers in separate incidents in 2010 and 2013.
"Zookeepers and cleaners should follow the procedure to keep carnivores in a separate place when cleaning the animal cages," Xinhua's report on the latest incident cited unidentified commentators as saying.