Dietary supplements intended for adjunct treatment of inflammatory bowel diseases can play a significant role in treating these conditions due to the presence of various biologically active substances. They are also increasingly used to boost the intake of essential vitamins and minerals. Still, due to less stringent regulatory requirements and insufficient control, there is a risk of contamination and side effects. This study aimed to assess the quality of dietary supplements by measuring the mercury concentration in these products. Mercury and its compounds are among the most toxic environmental contaminants. Exposure to even small amounts of mercury can cause serious health problems, including mutagenic and teratogenic effects, oxidative stress, mitochondrial dysfunction, and toxicity to the central and peripheral nervous systems, as well as the kidneys. For these reasons, it is necessary to determine potential mercury contamination. The mercury concentration in the tested dietary supplements was determined using atomic absorption spectrometry with a mercury analyzer. This method was chosen for its speed and simplicity. The research results were compared with the maximum allowable mercury level in dietary supplements set by various regulatory bodies. All analyzed dietary supplements meet the requirements, meaning the mercury levels are below the maximum permissible level, except in two justice samples. The analysis of the results also showed that the calculated values of hypothetical mercury intake in the case of weekly use of the tested products do not exceed the PTWI (provisional tolerable weekly intake). Still, after orally administering two samples, the PDE values were determined to be above the permitted ones. In the conclusion of this work, the importance of constant control of the mercury content in commercially available food supplements is emphasized.