"Kitti’s hog-nosed bat, also called the bumblebee bat, is the smallest mammal, measuring about 3.1 cm (1.2 in) long and weighing about 2 gm (0.07 oz)"
I guess that means both the above ans are correct :D
Supplement from 06/15/2006 09:16am: The Etruscan Pygmy Shrew or White-toothed Pygmy Shrew (Suncus etruscus) is the smallest known mammal by mass, weighing only about 2 grams.
It is said to be lighter than the Bumblebee bat. The skull of the Bumblebee Bat, at 11 mm, is smaller than that of any other mammal.
Debatable as to whether mass or skull size determines the smallest mammal
Supplement from 06/15/2006 09:18am: The shrew is also the smallest by length!
Guiness world records:
Kitti's hog-nosed bat (Craseonycteristhonglongyai), also called the bumblebee bat, has a wing span of about 160mm 6.3 in and weighs 1.75 - 2g 0.06-0.07oz.
The smallest land mammal in terms of length is Savi's White-toothed pygmy shrew, also called the Etruscan shrew (Suncus etruscus), which has a head and body length of 36-52mm 1.32-2.04in, a tail length of 24-29mm 0.94-1.14in and weighs 1.5-2.5g 0.05-0.09oz.