Mytilus galloprovincialis, the Mediterranean mussel, is an important shellfish species that constitutes the majority of production and consumption among bivalve mollusks in Turkey. Since shellfish can accumulate toxic chemicals from seawater, it is important to monitor bioaccumulation from their natural beds. For this reason, in this study, the aim was to monitor the levels of dioxins and dioxin-like polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and toxic metals (Pb, Cd, and Hg) in M. galloprovincialis collected from the southern coast of the Marmara Sea from 2014 to 2017. According to the results, the maximum levels of dioxins, PAHs, and toxic metals during the monitoring period were determined as 0.30 pg/g, 2.52 mg/kg, and 0.43-0.34-0.76 (Pb-Cd-Hg) mg/kg, respectively. Dioxin, PAHs, and toxic metal amounts in mussel samples were determined to be below the threshold levels enforced by the European Commission. The highest benzo(a)pyrene and total PAHs were determined in winter 2015, while toxic metals, dioxins, and dioxin-like PCBs (WHO/PCDD/F-PCB-TEQ) were higher in autumn 2014 than the rest of the sampling period. In conclusion, toxic chemicals monitored in M. galloprovincialis were found at low concentrations from the point of view of food safety. However, monitoring of these or other toxic chemicals should be repetitively performed in the future to ensure food safety in aquatic animals.