The Hornby's Storm-petrel or Ringed Storm-petrel (Oceanodroma hornbyi) is a seabird that ranges in the Humboldt Current off the coasts of South America. The species is a very distinctive member of the storm-petrel family, with a dark cap, white face and underparts, forked tail and a black band across the chest. It is relatively common in the seas off Peru, Chile and Ecuador. The species is named after Admiral Phipps Hornby.

The breeding biology of the Hornby's Storm-petrel is a mystery, as its colonies and nests have never been found. It is thought to breed between March and July, as this is when fledglings are regularly seen at sea around Lima (in Peru) and Antofagasta (in Chile). There have also been reports of mummified fledglings and adults found in crevices in the Atacama Desert 50 km from the sea, and even reports of one fledgling being seen 150km from the sea, and one unproven report of a bird flying into a nest in the town of Caraz in Peru, 100km from the sea.

It is difficult to know how threatened, if at all, the Hornby's Storm-petrel is. At sea estimates put the population in the thousands or tens of thousands. Recently a vagrant Hornby's was seen off the coast of California by a team from NOAA.

The name of this bird commemorates Admiral Sir Phipps Hornby.

A Hornby's Storm-petrel at sea, showing the distinctive black band and cap.