In a release, the zoo said the male was found by animal care staff at about 7:30 a.m. PT. The animal was previously considered healthy.
Jafari arrived at the Greater Vancouver Zoo in 2001 at six months of age.
"This is extremely hard on all of us at the zoo, although we take comfort in knowing visitors of the zoo had an opportunity to learn more about this beautiful endangered species," said spokesperson Jody Henderson.
The cause of death is not known and a necropsy will be performed.
Jafari is the third giraffe to die at the Greater Vancouver Zoo in the past year.
Two giraffes died within a week in November 2011 — both three-year-old Amryn and 23-year-old Eleah were found dead inside their barns.