Ross Castle (Irish: Caisleán an Rois) is a 15th century tower house and keep on the edge of Lough Leane, in Killarney National Park, County Kerry, Ireland. It is the ancestral home of the O'Donoghue clan,though it is better known for its association with the Brownes of Killarney who owned the castle until more recently.

The castle is operated by the Office of Public Works, and is open to the public seasonally with guided tours.
Ross Castle was built in the late 15th century by local ruling clan the O'Donoghues Mor (Ross), though ownership changed hands during the Second Desmond Rebellion of the 1580s to the MacCarthy Mór. He then leased the castle and the lands to Sir Valentine Browne ancestor of the Earls of Kenmare. The castle was amongst the last to surrender to Oliver Cromwell's Roundheads during the Irish Confederate Wars, and was only taken when artillery was brought by boat via the River Laune. Lord Muskerry (MacCarty) held the castle against General Ludlow who marched to Ross with 4,000 foot soldiers and 200 horse; however, it was by water that he attacked the stronghold. The Irish had a prophecy that Ross could never be taken until a warship could swim on the lake, an unbelievable prospect. The sight of the 'ships' unnerved the onlookers and the castle soon submitted.

At the end of the wars, the Brownes were able to show that their heir was too young to have taken part in the rebellion and they retained the lands. By about 1688, they had erected a mansion house near the castle, but their adherence to James II of England caused them to be exiled. The castle became a military barracks, which remained so until early in the 19th century. The Brownes did not return to live at Ross but built Kenmare House near Killarney.

There is a legend that O'Donoghue leaped or was sucked out of the window of the grand chamber at the top of the castle and disappeared into the waters of the lake along with his horse, his table and his library. It is said that O'Donoghue now lives in a great palace at the bottom of the lake where he keeps a close eye on everything that he sees.