The gens Opellia, also spelled Opelia and Opilia, was a minor family of imperial Rome, which briefly emerged from obscurity when Marcus Opellius Macrinus was proclaimed emperor following the murder of Caracalla in AD 217. The only members of this gens who appear in history are the emperor and his son, Marcus Opellius Diadumenianus, who ruled briefly as co-emperor in 218, but other Opellii are found in inscriptions, particularly from Dacia.