Thousands of passengers were braced for disruption ahead of a 48-hour walkout over pay and conditions.
On Wednesday, Ryanair lost a last-ditch legal challenge in the UK to stop the strikes.
But the low-cost carrier has said it will aim to minimise disruption for passengers and will be able to run its “full schedule of flights”.
The airline said it had drafted in pilots from elsewhere in Europe to fill in during strike action.
Ryanair said it would inform passengers of any changes to their flights by email and text message. “If you have not received any SMS or email from us, your flight is scheduled to operate,” it said. Customers can also check its website.