Papyrus Oxyrhynchus 21 is a fragment of the second book of the Iliad, written in Greek. It was discovered by Grenfell and Hunt in 1897 in Oxyrhynchus. The fragment is dated to the first or second century AD. It is housed in the Institute for the Study of Ancient Cultures at the University of Chicago. The text was published by Grenfell and Hunt in 1898.