Boo Boo
, a Chihuahua stands at just four inches (10.16cm) tall, is the world's smallest dog in height, according to the Guinness Book of World Records.
Boo Boo's owner, Lana Elswick, breeds Chihuahuas, and said Boo Boo was the size of her thumb when she was born. It hasn't got much bigger since being born a year ago, weighing just 42.5 grams (1.5 ounces).
Source: Boo Boo is world's smallest dog @ BBC
Read also: Great Dane -World's tallest Dog, Elwood, World's Ugliest Dog