Leiobunum rotundum is a species of harvestman. It is found in the western Old World.

Leiobunum rotundum is chestnut-brown, with a very long round or oval body and thin black legs. There is no separation between the head and the abdomen. The body is smooth and small. The harvestman's legs can be self-amputated if it is in danger of predation, but they do not regenerate. Although the harvestman has no fangs, poison glands, or silk glands, it can protect itself with the scent glands on the front of its body. The scent glands produce a secretion that repels predators. The species has three different types of nephrocytes. Numerous large nephrocytes occur in clusters between the muscles in the anterior region of the body. Smaller nephrocytes are scattered throughout the body, often stuck to tracheoles. The third type of nephrocyte is attached to the heart wall by connective ligaments. The morphology of the tracheae in this species is very similar to that of Nemastoma lugubre.

The harvestman eats a wide range of small invertebrates, alive or dead. Small invertebrates that it eats include caterpillars, mites, woodlice, and slugs. It drinks a lot of water, especially dew. It will sometimes suck the juice out of overripe or bruised fruit such as windfall apple. The harvestman will sometimes go to outside lights to eat insects that are attracted to the light.