In May alone, Zagreb Airport served 399,730 passengers, up 21.3% on the year, ADP said in a press release on Monday.
Aircraft movements at the airport increased by 10.3% on the year to 19,437 in the January-May period.
In May, the figure reached 4,511, up 12.7% on the year.
ADP and Turkey's TAV Airports, 46%-owned by ADP Group, hold stakes of 21% and 15%, respectively, in airport operator Zagreb Airport International Company (ZAIC).
In 2012, the Croatian government and ZAIC signed a 30-year concession contract for the management of the airport and the construction of a new terminal. The remaining shareholders in ZAIC are France's Bouygues Batiment International with 20.8%, EU-backed Marguerite Fund with 20.8%, IFC with 17.6%, and Croatia's Viadukt with 5.1%.