The Irish carrier said that one of the continent’s biggest success stories had been airline deregulation, which brought about cheaper fares for passengers.
While Ryanair is critical of both the UK government and EU it still favours the status quo.
The airline gave a number of reasons why staying in the EU was critical for the UK, including: jobs growth, the open skies agreement and the fact that investment could be lost to the likes of Ireland and Germany.
Chief executive Michael O’Leary said: "As the UK’s largest airline, Ryanair is absolutely clear that the UK economy and its future growth prospects are stronger as a member of the European Union than they are outside of the EU.
"Leaving Europe won’t save the UK money or red tape because like Norway the UK will still have to contribute to Europe, and obey its rules if it wants to continue to trade freely with Europe, so it’s clear that UK voters should vote Yes to Europe and Yes to the reformed Europe, that David Cameron has delivered."
Ryanair joins rival easyJet, whose chief executive Carolyn McCall has already called for the UK to stay in the EU.
