The strikes are the latest in a series of walkouts by staff at Europe's largest low-priced airline.
The Dublin-based carrier said that it would cancel six per cent of flights amid the walk-outs in Belgium, Italy, the Netherlands, Portugal and Spain.
Ryanair shares are lower Friday, as the budget Irish airline has cancelled 250 flights from its Friday schedule due to strike action.
The airline said it expected 90% of its flights to run as scheduled, and that replacements or refunds have been offered to affected passengers.
The carrier says about 35,000 of its 450,000 passengers have been affected by the disruption brought by the two strikes.
Joining in the industrial action, the Vereinigung Cockpit (VC) called on Ryanair pilots in Germany to strike from 3.01am (German time) on Friday to 2.59am on Saturday.
Ryanair will cut 150 flights because of strike action across Europe on Friday, as Brussels urged it to respect workers' rights enshrined in European Union law.
"We find this strike... unreasonable and somewhat out of sync with the progress we thought we were having", Ryanair COO Peter Bellew said in a conference call with journalists on Thursday.
Staff claim this creates huge insecurity for them, blocking their access to state benefits in their country.
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Earlier this month Ryanair chief executive Michael O'Leary said strikes by pilots were necessary to keep air fares down.
The German pilots' union said it could not rule out further strikes.
Tensions ran high at Eindhoven Airport in the Netherlands where some passengers had already passed through security when a flight to London was canceled with just half-an-hour until take-off.
Germany's services union Verdi, which represents around 1,000 cabin crew at Ryanair, has said its members would hold rallies on Friday.
The European Commission said Ryanair employees should have contracts in the countries where they live rather than in Ireland, where its planes are registered.
Another indication of the company's rethink on contracts came on Thursday when it announced two new bases in France.
"Respecting EU law is not something over which workers should have to negotiate, nor is it something which can be done differently from country to country", Ms Thyssen said.
Ryanair, which now has 86 bases, aims to fly 200-million passengers per year by 2024, up from a forecast of 139-million in 2018.