The dietary supplement market in Poland has been growing rapidly, and the number of registered products and their consumption increases steadily. Among the most popular and the easiest to get are herbal supplements, available in any supermarket. The aim of this paper was to investigate the mercury content in the herbal supplements. The dietary supplements that have been examined (24) are available on the Polish market and contain one or more herbal ingredients. Supplements were pulverized in porcelain mortar and identified by AMA 254 atomic absorption spectrometer. The range of variations for all tested supplements was within 0.02–4293.07 μg/kg. The arithmetic mean of the total result was 193.77 μg/kg. A higher mercury content then this mean was found in preparations—bamboo shoots and alga Chlorella pyrenoidosa. The studies have shown that mercury is present in every examined herbal supplement, and its content exceeds in two preparations (with bamboo and alga) the permissible limit of 0.10 mg/kg. There were statistically significant differences in the occurrence of mercury depending on the herbal ingredient in the supplement. The lowest content was found in the preparation with Tanacetum parthenium and the highest with bamboo shoots. The mercury content in the tested herbal supplements was statistically significant in the form of a supplement—a tablet and a capsule. Daily, weekly, monthly, and yearly consumption of mercury with examined supplements was calculated—the results did not exceed the PTWI—provisional tolerable weekly intake of mercury. To increase consumer safety, it is imperative to conduct further research on dietary supplements and implement a stricter quality control of the dietary supplements.