Megalomys is a genus of rodent in the family Cricetidae, part of the tribe Oryzomyini. The genus contains five large rodents from various Caribbean islands, all of which are now extinct. The last species to survive was M. desmarestii from Martinique, which became extinct after the Mount Pelée eruption in 1902. Ancient DNA analysis places Megalomys forming a clade with Pennatomys, sister to the clade containing Aegialomys, Nesoryzomys, Melanomys and Sigmodontomys, having diverged from the mainland clade around 7 million years ago.