Animal rescuers in northern California said the female Dachshund mix, named Beyonce, was so small at birth that she could fit into a spoon. At two weeks, she is about the size of a business card.
The Grace Foundation, based in El Dorado County, says animal control officers picked up Beyonce's pregnant mother, and she gave birth to a litter of five on March 8.
Beyonce was the last one delivered, and was born without a heartbeat. Vets managed to revive her through chest compressions and mouth-to-mouth resuscitation.
The foundation says she will be ready for adoption in about two weeks.
It has submitted an application to Guinness World Records for the world's smallest dog.