The context of progressing European integration and the increasing cross-border transformations of corporate entities, in particular, cross-border conversions of companies have become a significant legal instrument enabling flexible corporate restructuring within the European Union’s internal market. The aim of the article is to assess the effectiveness of creditor protection mechanisms in the process of cross-border transformation of a capital company, with particular emphasis on the structure of security for claims provided for in Article 580¹² of the Commercial Companies Code. The article attempts to answer the question of whether the applicable regulations ensure an appropriate balance between the protection of creditors’ interests and the implementation of the principle of freedom of establishment and mobility of companies within the European Union’s internal market. The author examines selected legal aspects of the liability of the converting company to the creditors during the process of a cross-border conversion. The focus is on the mechanism of creditor protection provided under Article 580¹² of the Polish Commercial Companies Code, which allows creditors to seek adequate security for their claims, provided that a risk of non-satisfaction can be substantiated. The article further explores the institutional framework of the conversion procedure, with special attention to the role of the court in assessing the legitimacy of creditor claims.