"I reached down and grabbed the cane toad and couldn't believe how big and heavy it was," ranger Kylee Gray said.
The rangers nicknamed their discovery "Toadzilla" and removed it from the park due to the danger it could pose to the environment.
"A cane toad that size will eat anything it can fit into its mouth, and that includes insects, reptiles and small mammals," Gray said.
She said the toad, believed to be a female, weighed in at 5.9 pounds, which could be a new record for the species.
"I'm not sure how old she is, but cane toads can live up to 15 years in the wild -- so this one has been around a long time. We're pleased to have removed her from the national park," Gray said.
She said The Queensland Museum has shown interest in taking Toadzilla for further study.