Gesomyrmex magnus is an extinct species of formicid in the ant subfamily Formicinae known from a fossil found in eastern Asia.

Located in the Pozharsky District, on the Pacific Coast of Russia, the fossil-bearing rocks preserve possibly Priabonian plants and animals which lived in a small lake near a volcano.

The fossil, a nearly whole winged queen in dorsal view, was first described by the trio of paleomyrmecologists Gennady Dlussky, Alexandr Rasnitsyn and Ksenia Perfilieva.

[1] The holotype queen is approximately 20.5 mm (0.81 in) with a fore-wing partially preserved and the hind-wings absent from the fossil.

The legs are short and have a thick appearance, while the gaster oval in shape and the fore-wings were approximately 12.5 mm (0.49 in) long.