The month-old male giraffe died around 5 p.m. Sunday night.
Zoo staff say the giraffe died after running into a fence during a special preview event for the new "African Adventure" exhibit.
Two veterinarians rushed to the scene, but it was too late.
The giraffe was born in the enclosure and officials say should have been familiar with the environment.
"It's really, we've had the exact same-type situation in their exhibit for a decade, in their old exhibit, and so for this to become an issue was really a surprise, but it is one we are dealing with," said Scott Barton, Fresno Chaffee Zoo.
A zoo spokeswoman says a necropsy will be performed to determine the exact cause of death.