No, UGGS are unfortunately not Vegan. The outside of the stylish and comfortable winter boots are made from from Twinface sheep skin, which is leather so not Vegan at all.
The other materials are fleece (a 100% synthetic fabric) for the inside of the shoe and the sole is made from a synthetic material as well.
Are you are looking for a similar pair of boots with the same stylish look and as comfortable as the original UGGS without the use of animal materials, check out the UGGS Vegan alternatives page.