As the level of development increases, spatial planning is becoming more significant among public management tools. Although the issue of spatial planning and its mechanisms has been repeatedly investigated in the literature, the issue of clashing of interests of different actors remains to be examined. Therefore, the aim of this study was to compare the enforcement mechanisms of the public interest in the spatial planning systems of Poland and Portugal. The analysis was based on a comparative analysis of the legal basis of the spatial planning systems of the countries. The research confirmed the hypothesis that even with some sociocultural and economic similarities, different countries do not have to create similar mechanisms for the realisation of the public interest in spatial planning processes. The specific solutions adopted in Poland and Portugal differ so much that the enforcement of the public interest proceeds with very few similarities. The integrated Portuguese planning system, with its hierarchical elements, facilitates the achievement of the objectives of public entities. On the other hand, the Polish system, with the dominant position of the municipality, pushes great possibilities of influencing the planning by land administrators, and the poor location of spatial planning in all public tasks makes it difficult, and sometimes even impossible, to achieve public goals in space.