The woman driving the car only became aware of the kitten when she heard repeated squeaking.
She was travelling from Cornwall to London and stopped the car at Staines, Surrey, when the squeaking made her think there was a mechanical problem.
The AA mechanic who came to fix the car found the kitten under the bonnet and brought her to the Willett House vets in Staines.
Sarah Watkins, from the surgery, said: "There's absolutely nothing wrong with her."
The kitten is described as a tortoise-shell, between 8-10 weeks old and has not been microchipped.
A kitten travelled more than 200 miles (322km) trapped under a car bonnet.