This paper, entitled " Invasive alien animal species in Croatia ", focuses on the ecological and economic effects of non-native invasive species introduced to Croatia, intentionally or accidentally. Invasive species, which include insects, mammals, fish, crabs, reptiles and birds, adapt quickly and more widely due to the lack of natural predators, endangering local biological diversity and disrupting ecosystems. Various habitats in Croatia, from forests, rivers and lakes to coastal and mountainous areas, provide good living conditions for new species. Croatia's diverse climate and climate change further favors their survival and expansion. Human activities such as trade, tourism and transport also contribute to the spread of invasive alien species, with ports such as the one in Rijeka being significant entry points that are not sufficiently controlled. The paper also discusses the classification of invasive species based on their impact. The European Union Regulation (EU) no. 1143/2014 aims to prevent and manage the introduction and spread of invasive species. The basis of that Regulation is the „Union's list“ of invasive alien species that cause concern in the European Union and in Croatia as well. Species are categorized into black, gray and white lists depending on the level of danger. Examples of invasive species in Croatia are studied with a detailed explanation of their origin, method of introduction and specific ecological damage they cause. The paper emphasizes the importance of recognizing and reduction of the impact of invasive species for the preservation of Croatian indigenous biodiversity and the preservation of ecological balance.