Struthiomimus was an "ostrich-mimic" theropod , similar in size and appearance to modern ground birds such as ostriches and emus.

Ornithomimids such as Struthiomimus are believed to be the fastest of dinosaurs. Some studies indicate that they may have been able to run faster than ostriches at speeds in excess of 75 kph.

The diet of ornithomimids has been unclear to scientists for some time. Eggs, small animals, and insects have all been suggested as possible food items. Although such things may have formed part of their diets, it is likely that ornithomimids ate fruit, seeds and plants more often. The discovery of gastroliths in an ornithomimid skeleton suggests that they may have been able to digest tougher vegetation than previously thought.

Struthiomimus would have been in danger from the large tyrannosaurids that lived in its area.