Gallimimus or Gallimim is an Struthiomimus dinosaur from Asia that lived in the Late Cretaceous period in what is now Mongolia about seventy million years ago. Its name means "chicken mimic". Individuals of gallimimium reached 8 meters in length, which makes it one of the largest known Ornithomimus.

Visually, the gallimim looked very much like an ostrich: a small head, large round eyes, a toothless beak, a long neck, short fore and long hind legs, as well as a long tail. The dinosaur waved this tail side to side while running to maintain balance. Some scientists even suggest that Gallimimus was a feathered dinosaur. Scientists are still arguing over what the Gallimimus ate. Most paleontologists tend to believe that these dinosaurs were omnivores. A very mobile neck may have helped detect small prey on the ground, but it could also have been an opportunistic omnivore. It has also been suggested that it used small columnar structures in its beak to filter food in water, although these structures may instead have been combs used to feed on tough plant material, suggesting a herbivorous diet.

The first fossils of this dinosaur were discovered in 1963 by a team of researchers during a Polish-Mongolian expedition in the Gobi Desert in Mongolia.