The aim of the publication is to establish the function of the legal regulation of the principle of resolving legal doubts in favour of the citizen (in dubio pro libertate), introduced by the amendment of 2017 to the Code of Administrative Procedure. The purpose of the article is also to compare the state of the regulation in force at the time of its entry into force with the legal state created after the introduction of the amendment. This principle has been discussed and it has been established that it has a protective function. First and foremost, to ensure the security and stability of the law when the legislator has failed to fulfil its duty to legislate correctly and fairly. This function is of particular importance in cases where an administrative body unilaterally determines constitutional rights and freedoms. As a result of the comparison of the state of regulation before 2017, it was established that as long as the principle of in dubio pro libertate was a postulate of the doctrine, court judgments, interpreted from other principles of administrative proceedings, it did not suffer such significant limitations and could serve more fully to protect an entity. It the current state of law, administrative bodies can make use of it in a limited way only to several proceedings. Nor does it apply if there is – as is common in administrative proceedings – an important social interest or conflicting legal or factual interests of the parties concerned.