Green intellectual capital (GIC) is a distinctive intangible asset that may assist organizations in pursuing sustainable development strategies. In Polish organizations, interest in this new concept is low. Analysis of the literature showed a lack of research regarding the implementation of GIC practices or their impacts on the sustainable development of organizations in Polish enterprises. In order to fill the detected research gap, the study covered 150 randomly selected Polish enterprises. The purpose of the research was to determine the impact of activities fostering GIC on the environmental development of companies in Poland and to identify major practices supporting GIC development. In addition, the author attempted to establish a correlation between the impact of individual practices oriented at GIC formation and their practical implementations in the analyzed enterprises. The first stage of the analysis focused on identification of activities leading to the accumulation of GIC implemented in Polish organizations. The second stage involved an assessment of the level of impact of actions contributing to GIC formation on the environmental development of the studied enterprises. During the third stage, the author investigated the relationship between the impact of individual practices oriented at GIC formation and their practical implementation in the analyzed organizations. The study demonstrated that actions supporting GIC formation have an uneven impact on corporate environmental development. Among the key factors identified by the author were environmental attitudes of employees in the working environment (such as paper and energy saving), environmental knowledge, and the implementation of innovative environmental projects. Furthermore, the author established a correlation between the impact assessments of activities leading to GIC accumulation and their practical implementations. The research demonstrated that activities assessed by respondents as more important are more often implemented in practice. The findings of the research may stimulate interest in GIC development and extend the scope of application of GIC-fostering practices over organizations operating in the energy sector.