The topic of this thesis is the impact on the environment of the Rijeka Oil Refinery. The introductory part briefly describes the development of the oil industry in Rijeka, the concept of a refinery, and how the first refinery in this area was founded. A description of the Rijeka Oil Refinery and its facilities and internal infrastructure is given. The main part of the paper describes the impact on the environment produced by the Refinery, the environmental protection measures that are implemented and the description of the existing system for monitoring the state of the environment. An overview of the environmental impact assessment procedures for the modernization of hydrocracking complex facilities and auxiliary units and for the production and processing of oil - coking complex is given. Spatial plans are the basis of the development and modernization of the Refinery, so a presentation is also given valid spatial planning documentation for the area where the Refinery is located, which includes the Spatial Plan of the Primorje-Gorski Kotar County and the Spatial Development Plan of the Municipality of Kostrena. It is concluded that the implementation of environmental protection measures resulting from the Act and by-laws, as well as those prescribed by public law bodies and those resulting from the implemented environmental impact assessment procedures, was effective because the negative impacts on individual components of the environment were reduced, and the air in the vicinity of the Refinery is of the first category.