The worker had been dropping off an order at a home when a rattlesnake coiled up at the door.
She placed the package by the front door of the home when the Eastern Diamondback Rattlesnake bit her in the back of her leg right above her knee, according to Martin County Officials.
This type of snake is known for being the most dangerous and venomous snake in North America.
The woman immediately became ill and called 9-1-1.
She was taken to a hospital in Palm City where she is in very serious condition.
Officials were able to catch the snake that attacked her.
They say these rattlesnakes are quite common in the area.
CNN contributed to this report.