U radu se analizira uređenje poništavanja rješenja kao pravne sankcije protiv nezakonitih i nepravilnih akata u upravnom postupku. U uvodu se daje kraći prikaz temeljnih pojmova i koncepcija: pogrešnih akata, nezakonitih i nepravilnih akata, ništavih i oborivih akata, netočnih akata, presumpcije valjanosti upravnog akta te sankcija poništavanja i ukidanja nezakonitih i nepravilnih upravnih akata. U nastavku se analiziraju svi ZUP-om propisani slučajevi poništavanja rješenja u prvostupanjskom i drugostupanjskom upravnom postupku, u postupcima u povodu izvanrednih pravnih sredstava te u postupku izvršenja. U zaključku se u kraćim crtama iznose osnovne teze iznesene u radu te se zalaže za normativno uređenje poništavanja rješenja u upravnom postupku kojim bi se u cijelosti slijedila načela razmjernosti i zaštite stečenih prava stranaka u upravnom postupku. The paper analyses the regulation of annulment of decisions as a legal sanction against unlawful and irregular acts in the administrative procedure. The introduction gives a brief presentation of basic terms and concepts: wrong acts, unlawful and irregular acts, void and rebuttable acts, incorrect acts, presumption of the validity of the administrative act and the sanctions of annulment and revocation of unlawful and irregular administrative acts. Further in the paper, all the cases of annulment of decisions in first and second instance administrative procedures prescribed by the Code of Administrative Procedure are analysed, in procedures on the occasion of extraordinary appeal and in the execution procedure. In the conclusion, the basic theses elaborated in the paper are briefly presented and the conclusion advocates for the normative regulation of annulment of decisions in the administrative procedure that would fully follow the principles of proportionality and the protection of acquired rights of the parties in the administrative procedure.