The bite occurred Wednesday afternoon at the Matthaei Botanical Gardens. The girl was taken to C.S. Mott Children's Hospital.
Diane Brown, a spokeswoman for the University of Michigan's department of public safety, said she did not know what condition the child was in.
The university received a grant in 2012 for habitat restoration for the rattlesnake in the botanic gardens. Signs now warn visitors that the eastern massasauga is present, Brown said.
The snake is one of the smallest of North American rattlesnakes, with adults growing to be about 30 inches long. The Michigan Department of Natural Resources says on its website that bites are rare and almost never fatal.
"It is best to treat them with respect and leave them alone," the DNR said. "The few bites that occur to humans often result from attempts to handle or kill the snakes."