The little lives were saved by vet Emma Owen, who operated when she realised Ruby would be unable to give birth naturally.
The cat, whose Maine Coon breed is native to America, is only eight months old.
Emma said: “None of the kittens were moving or had heartbeats during the surgery.
“It was a great relief to find all nine survived after revival by our team of nurses and vets, who all jumped in to help.
“The owner was so pleased and couldn’t believe there were so many kittens from such a small, young mother.”
Monika Gorna, from Totton, Hampshire, took Ruby to the vets last month when she noticed her pet’s belly was swollen.
She had no idea that Ruby was pregnant as she believed she was too young.
However, an ultrasound at the Seadown Veterinary Group clinic revealed the nine kittens.
She took Ruby back to the practice last week when the animal was unable to give birth naturally, with Monika initially hoping that Ruby would survive.
The 31-year-old public servant said: “My main concern was for the welfare of Ruby, as the vets had said the kittens might be dead as the first one was blocking the way out.
“So I couldn’t believe it when they told me I had nine live kittens, five boys and four girls.
“They are all healthy and I have taken them home.”
She added: “As the mother is so young she is not producing much milk so I have been hand-feeding the kittens every two hours with the help of my stepdaughter.
“I haven’t had much sleep for the past couple of days and am absolutely exhausted, but the kittens are doing well and are now quite playful.
“I am grateful to the vets and nurses – they truly are miracle workers.”
Miss Gorna said she would love to be able to keep all nine kittens, but as she already has 12 cats she will only keep one – and find good homes for the other eight.