Review. The article defines the element of admissibility as the primary characteristic of the evidence in administrative offences and provides criteria and functions of admissibility. On the basis of the provisions of the General Part of the Administrative Code, clarifications of the Supreme judicial bodies, judicial practice concerning administrative offences in the sphere of environmental protection, the author justifies the conclusion that it is necessary to categorize violations committed during administrative proceedings and determines the grounds for recognizing their materiality that entail the loss of effect for the evidence. The methodological basis of the research is formed by general scientific (dialectical materialistic analysis and synthesis) and specific scientific (systematic structural, comparative legal, statistical, formal and legal) methods of scientific cognition. The research brings about the conclusion that declaration of inadmissibility of evidence is connected with determination of gravity of law violations with regard to their materiality that casts doubt on the information acquired, determination of a grave violation of the Administrative Code provisions aimed at the protection of rights of an individual against whom administrative proceedings have been initiated or against other participants of administrative proceedings. The author provides proposals for supplementing the Administrative Code with legal norms governing the procedure of recognizing the evidence inadmissible.