Authorities say the man illegally entered the Fresno Chaffee Zoo just after 11 p.m. and went into the African Adventure Exhibit area.
Police say he climbed over a fence into the lions' enclosure, where one lion bit his left foot.
Security was able to detain the man, who only suffered minor injuries.
The man reportedly claimed he was being chased by someone.
Zoo staff said that in the three years that the African Adventure exhibit has been open, something like this has never happened.
"He did have to jump over the fence that has a no trespassing sign, and (he) climbed over the barbed wire on top of it to actually get into the zoo itself," Fresno police Lieutenant Jennifer Horsford said.
Police found drug paraphernalia on him and believe he was under the influence. The man will be cited for trespassing.
Police are still investigating whether the man was being chased.
Veterinarians at the scene say the lions were not harmed.
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