The oppositional grounds of appeal regulated by the Enforcement Act will be discussed in this dissertation. The introductory chapter provides considerations on the legal remedies available to the parties in the enforcement proceedings, the oppositional grounds of appeal, and the rights that enforcement debtor and party seeking enforcement have in the event of an oppositional ground of appeal. The second chapter presents the definition of an appeal in enforcement proceedings and the court's actions when receiving an appeal. The third chapter presents the general grounds for appeal in enforcement proceedings and who is authorized to file an appeal and when. The following chapters explain in detail the reasons for opposition appeals, what happens when they appear, when the enforcement debtor and party seeking enforcement can point them out, and when they can file an opposition lawsuit. The eighth chapter presents several examples from case law in the Republic of Croatia. In the conclusion, the author emphasizes the most important thoughts on the grounds of appeal, and oppositional grounds of appeal and presents her opinion on the judgment presented in this dissertation.