The ceremony will be held in Zagreb and Split, with top Croatian officials, including President Stjepan Mesic, Sabor Speaker Vladimir Seks and the mayors of the two biggest Croatian cities, attending.
Prime Minister Ivo Sanader will officially cut the red ribbon at Skradin, in the hinterland of the coastal city of Sibenik.
Former and current officials who have advocated the building of the motorway connecting the country's north and south, will also hold speeches at Skradin. Among them are Savka Dabcevic-Kucar, Zlatko Matesa and Ivica Racan.
The Mala Kapela tunnel, the longest tunnel in Croatia, which is part of the highway, was opened to traffic at 10:00 am Friday.
The 5,780-kilometre tunnel connects two sections of the Zagreb-Split highway - one runs from Josipdol to the Mala Kapela tunnel and the other runs from the Mala Kapela tunnel to Zuta Lokva.
The northern entrance to the tunnel is at an altitude of 562 metres and the southern entrance is at an altitude of 573 metres.
The speed limit for vehicles passing through the tunnel is 80 kilometres per hour.
The construction of the tunnel cost about 550 million kuna. The Italian CoopcostruttorI company started and the Croatian Viadukt company finished its construction.
Citizens can use the entire highway as of early Monday. The road toll is 157 kuna.
The construction of the Zagreb-Split highway, the A1 highway, was one of the biggest construction and investment projects in Croatia. The cabinet of former Prime Minister Ivica Racan adopted the decision on the construction of the highway in October 2001. The entire project is worth 17 billion kuna, excluding Value Added Tax, covering the construction of the 380 kilometre-long section on which a total of 292 facilities, namely 26 bridges, 50 viaducts, 91 overhead railroads, 78 underpasses, 25 passes, 14 tunnels and five crossings for animals, have been built.
(1 EUR = 7.3 kuna)