Well now you've met the smallest and the LARGEST dogs ever but, what about meeting the LARGEST and the smallest dog breeds ever? First of all the largest dog breed ever is the Great Dane. However the smallest breed of dog is the Chihuahua-my FAVORITE breed of dog in the whole wide world! Did you know that the Chihuahua is also the lightist dog in the world. But, just because the Chihuahua is both the lighrist and the smallest dog breed ever dosen't mean that the Great Dane is the largest and the heaviest dog breed ever. Turns out the swiss St.Benard is the heaviest dog.