The aim of this study was to determine the concentration of mercury (Hg) in liver (L), kidney (K), breast muscle [BM (musculus pectoralis major)], breast feathers (BF), and stomach contents (SC) of mallard (Anas platyrhynchos L. 1758). Among the edible parts of mallard, the greatest concentrations of Hg were observed in K and L, although they did not exceed 1.5 mg/kg dry weight (dw). Average concentrations in K, L, and BM were 0.27, 0.25, and 0.13 mg/kg dw, respectively. Significant correlations were observed between Hg concentrations in BM and K and in BM and L (r s = 0.92) as well as between Hg concentrations in these tissues and BF. In addition, we found significant correlations between Hg concentrations in SC and BM (r s = 0.72) and in L and K (r s = 0.55). In conclusion, mallard exhibits a measurable response to environmental Hg pollution and meets the requirements of a bioindicator.