Ryanair is selling up to 10 million new shares - around 2.8% of the company - while chief executive officer Michael O'Leary is selling 3 million of his ordinary shares.
News of the sale coincides with what the budget airline describes as a record third quarter.
The number of passengers rose by 39% to 1.9 million, whilst adjusted profits after tax rose by 42% to 21.3 million euros (£13.6 million), compared to the previous quarter.
Mr O'Leary currently owns 30 million ordinary shares or 8.5% of the issued share capital of the company.