During the period from 2019 to 2023, as part of the project to construct the state road D403 from junction Škurinje to the Port of Rijeka and the construction of access roads to the Pelješac Bridge, geological supervision was carried out over the excavation of the "Podmurvice" tunnel with a total length of L=1237.00 m and the "Debeli Brijeg" tunnel with a total length of L=2443.00 m. The role of geological supervision over tunnel excavation involved actively participating in the process of determining the actual engineering geological profile along the tunnel route and the process of verifying the stability of underground excavation. During the design phase, geotechnical classification of rock mass was applied using the RMR (Rock Mass Rating; Bieniawski, 1989) and Q-system (Barton, Lein, Lunde, 1974; Grimstad, Barton, 1993). During the excavation phase, in coordination with the supervisory authority, RMR geomechanical classification (Bieniawski, 1989) was adopted as the main and leading classification method of rock mass, all with the purpose of determining the actually executed category of rock mass excavation, which served as the main basis for determining the type of primary substructure assembly. The main goal of this article is to compare the predicted or designed conditions (engineering geological profile along the tunnel route, rock mass quality (excavation categories), types of primary substructure assembly, etc.) with the actually executed conditions at the mentioned locations of two recently constructed tunnels in the Republic of Croatia.