Companies of the construction sector face a significant impact on the environment and people: consume massive amounts of natural resources, emit pollutants, and generate large amounts of waste, are a place of danger and accidents at work. It is well established that implementation of CSR principles can lead to several economic, social, and environmental benefits. This is shown by numerous studies carried out in various countries among companies from different sectors of the economy. The aim of the article is to identify the most determining activity motives, barriers, and effects of implementing CSR principles by enterprises of the Polish construction sector and to determine the differences in this aspect between large, medium, and small-size enterprises. A questionnaire survey covered 177 enterprises. Factor like size, a place of origin, type of capital (domestic, foreign), annual turnover and time in the market were also considered. The documents of enterprises, reports, statistical data, and internal regulations of companies were also examined. The research results show large variations in terms of motives, barriers and expected benefits out of the implementation of CSR principles in various types of construction enterprises. There are different ways of implementing CSR principles and incorporating this area into organizational structures of the companies. A special role is assigned to large enterprises that show the greatest commitment in this scope. They become sources of good practices for other types of enterprises.