The American pygmy shrew is the smallest mammal native to North America and is one of the smallest mammals in the world, just slightly larger than the Etruscan shrew of Eurasia. Its body is about 2 in long, and it weighs about 0.07 to 0.16 oz. Its pelage is generally a reddish or grayish brown during the summer, and a white-gray color during the winter. The underside is generally a lighter gray. This animal molts about twice a year, once during late summer, and again during the spring. It has a narrow head with a pointed nose, and whiskers. The eyes are small and well hidden. The senses used for hunting are hearing and smell.

They prefers moist habitats, it has been recorded to live in areas with both wet and dry soil, but if it is living in a more arid environment, it needs to have a source of water nearby. The pygmy shrew is always hungry: it can eat 125% of its body weight every day! It mainly preys on insects, spiders and woodlice, but, unlike the common shrew, does not eat earthworms. It is a terrestrial mammal, preferring to live in areas with dense vegetation, which serve as protective cover. Since such conditions are easily met in many plant community types, S. minutus can be found in forests, woodland edge, shrubland, heathland, grasslands, wetlands, coastal sand dunes, and rocky areas.