The size of Campbell's dwarf hamster varies depending on its location. For example, eight wild specimens examined from Mongolia showed an average head and body length of 80 millimetres (3.1 in), an average hind foot length of 13.5 millimetres (0.53 in) and an average tail length of 5 millimetres (0.20 in).
In captivity, they are proportionally larger as commercial pet food and fruits provide more nutrition than food found commonly in the wild.
The lips and cheeks have white fur and the rest of the fur around the face can be either grey or brown. A dark and narrow dorsal stripe runs along the center of the back from the nape of the neck to approximately 2.5 centimetres (0.98 in) above the tail. The surface of the hands and feet are white to ensure that the animal stays warm in colder climates in countries such as Mongolia.
In both the wild and captivity, Campbell's dwarf hamster marks it scent around its territory using harderian glands, skin glands located behind the ears. It uses urine and feces for communication
Campbell's dwarf hamster is distinguished to the similar looking Djungarian hamster as it has smaller ears and no dark patch on the crown of its head.
The dorsal stripe of Campbell's dwarf hamster is narrower, shorter and darker than that of the Djungarian hamster and the fur on the stomach of Campbell's dwarf hamster is grey, but it is white on the Djungarian hamster.
Campbell's dwarf hamster does not turn white in the winter and has a grey tint to its fur. It has a smaller interorbital breadth but has a larger auditory bulla.
Campbell's dwarf hamster is much less tolerant to lower temperatures than the Djungarian hamster. The lowest tolerated temperature from a laboratory experiment showed that Campbell's dwarf hamster can resist temperatures as low as −31.8 °C (−25.2 °F), where the Djungarian hamster can withstand temperatures as low as −44.7 °C (−48.5 °F).
Campbell's dwarf hamster reacts to lower temperatures by constantly exercising and tries to find a sheltered location, unlike the Djungarian hamster which would curl up and rely on its thermo regulation.
Campbell's dwarf hamster has cheek pouches, which are an extension of the mouth.
Food is transferred into these pouches through the diastema. The inside of the pouch contains a large number of folds of dermal papillae. When the pouch is full, it extends and becomes part of the structure of the skin.
By eleven days of age, the cheek pouches are fully grown and can carry objects up to the size of a sunflower seed.
When the cheek pouches become full, they extend back to the shoulder blades, which restrict movement.
Campbell's dwarf hamster is prone to genetic abnormalities in the metabolism of carbohydrates and lipids.
They can develop tumors of the mammary glands, lungs, uterus and ovary. Tumors can also develop if the animal is exposed to chemical carcinogens.
Due to having a slow locomotion and an insignificant response to bright lights and humans, as well as having a low population density, field studies allow scientists to study entire populations in the wild.