Same Breed Only Smaller
People love the temperament of the Imperial Shih Tzu or miniature Shih Tzu. They are lovely family dogs who get along well with children and other pets. The life span is the same as the standard size ShihTzu. They are smaller because the breeders have carefully selected their breeding dogs to be more petite, this, of course, is the way all dog breeds have developed for centuries, selection by the breeder.

There is very little difference in the two as far as genetic makeup is concerned. The preferred size of the “Shih Tzu” was much smaller for the Chinese Royalty. In the Imperial palace, the Empress, Tzu, insisted that puppies that were too large to be accepted as an Imperial Dog were given away to less Royal members of society and foreign dignitaries. Having a royal dog to breed from was an honour, and no one knows how many ordinary people were producing them, but that’s how the modern ShihTzu originated.
By the time the Imperial Dog was introduced into the west, the size standard had begun to favour even bigger dogs. Lovers of Imperials generally prefer the shorter legs and bodies and flatter faces, with a smaller and lighter bone structure. You can also often see a lot more colours in the Imperials with a lot of Solid colours vs the party look of the standard ShihTzu.
See Here – History Of Chinese Imperial Dog

A true Imperial will be just as healthy, playful and fun-loving as any larger ShihTzu. Some misinformed people may suggest to you that they are all just the ‘runts’ of a standard litter, but this is false, they are bred to be smaller, and the whole litter will be of a smaller range than the standard breed.
Currently, the Kennel Club only recognizes the Imperial as a Shih Tzu because when the small Chinese breeds first came to the west, they were all lumped together as one breed. Consequently, they went on to be bred larger and larger and are now registered only as Shih Tzus. Many people are trying very hard to change this, however. In the US, the CID Club of America has developed its registry to better the breed and track their progress, and you can register a dog that qualifies by weight and size as an authentic Chinese Imperial.
Both Parents Should Be Imperial Shih Tzus!
If you are looking for a smaller Imperial puppy, you should be aware that some breeders are claiming to offer Imperial Shih Tzus when in fact they are not. To be a true Imperial Shih Tzu, both the mother and father should be a full Imperial or bred from smaller lines.
Tiny Teacup Imperial Shih Tzus
Not all Imperial Shih Tzu litters will have tiny teacups. Puppies are smaller in an Imperial litter, but there may be only one or two in the 7 pounds or under range. Some breeders will ask a higher price for these, however breeding too small can produce a girl that can not be safely bred from and if excessive, can produce puppies that need to be tube-fed. We are dedicated to healthy, happy puppies and therefor will not intentionally breed towards the excessively tiny puppies and have chosen our mums and dads carefully.