Megalograptus is a genus of eurypterid recovered from deposits of Ordovician age. The genus is classified as part of the Megalograptidae family and contains five species, four (M. ohioensis, M. shideleri, M. welchi and M. williamsae) from Ohio and one (M. alveolatus) from Virginia.

"Megalograptus" translates to "big writing" or "great graptolite" in Greek, a generic name that derives from that the first known fossils recovered of the genus were its spiny legs, which were mistaken for massive graptolites. Megalograptus was relatively large for an Ordovician predator, with the largest species (M. ohioensis) capable of reaching lengths of 78 cm (31 in). Other than its large size, Megalograptus is also of interest due to being one of the oldest known eurypterids in the fossil record.