The problem of microplastic in the seas is recognized as a global issue. The degradation of larger plastic items results in microplastics which, although invisible to the human eye, do not disappear through degradation but instead become a threat to marine organisms. In this form, it can easily enter the digestive systems of organisms and thus the entire food chain, causing harm to each organism. Awareness of the threats posed by microplastics to the lives of all organisms, especially marine organisms, is the starting point for the conducted research on common pandora (P. erythrinus) specimens from the Medulin Bay area in the southern part of the Istrian peninsula. The study included 31 samples of common pandora digestive tracts, from which 67 microplastic particles were isolated through laboratory processing. Among the isolated particles, based on the shape of the microplastics, fibers were the dominant form, and according to the color criterion, blue particles were the most prevalent (42.0%). The analysis also determined the proportion of filaments per individual per month of catch, leading to a conclusion about the correlation between the number of found microplastic fibers and the spawning period as well as sea temperature depending on the season. The results of the study indicate the presence of microplastic filaments in common pandora from Medulin Bay and potential contamination of the mentioned area, which can be caused by various sources of pollution. Certainly, when interpreting the research results, the possibility of sample contamination through the air during laboratory processing should also be considered. This points to the need for further research and continuous monitoring of both Medulin Bay and other protected marine areas.