| Named By: | R. J. G. Savage in 1973 |
| Time Period: | early Miocene 23.03-11.61 Ma |
| Location: | Africa, with countries including Egypt, Kenya, Libya, Namibia, Uganda |
| Size: | Largest known skull about 66 centimetres long. Overall roughly about 135 centimetres high at the shoulder |
| Diet: | Carnivore |
| Fossil(s): | Skull and postcranial remains |
| Classification: | | Chordata | Mammalia | Eutheria | Laurasiatheria | Creodonta | Hyaenodontidae | Hyainailourinae | |
Megistotherium (from Greek, megistos "greatest" + therion "beast" and osteon 'bone' + thlaston 'crushed, bruised' with -es being an agent noun: 'bone-crusher') is an extinct genus of hyaenodontid, the only known species of which is Megistotherium osteothlastes. It is most likely a junior synonym of Hyainailouros sulzeri