Background: Mercury (Hg) is considered a global pollutant because Hg0 which is the predominant form of atmospheric Hg resides in the atmosphere for as long as 0.5 to 2 years. Mercury has many negative effects on the reproductive, respiratory, and immune systems.Methods: In this study, 24 Caspian lampreys (Caspiomyzon wagneri) were transported to the university laboratory and then stored in -20oCuntil they were dissected. The liver, muscle, skin, ovaries, and testes were all dissected out. All samples were freeze-dried and ground by a mortar and pestle into powder. The specimens were analyzed by a Leco AMA254 mercury analyzer.Results: The order of mercury concentration in the lamprey tissues was as follows: Muscle>ovaries>liver>skin>testes. The mean values of mercury in muscle and testes were 192.25 ± 7.10 and 21.42 ± 1.48 Hg ng/g dry weight, respectively. There were no significant differences (N=24) between the sexes in the Hg level of most tissues except for gonads.Discussion: A comparison with some ammocoetes of jawless fishes shows a 10 times less concentration than other records. This difference probably is due to non-parasitic behavior and use of various sources of nutrition in other species.Conclusion: In comparison of other kind of sea lamprey, due to detritivore habits of Caspian lamprey on a very specific part of food web (non-live food only in the sea floor), the supposed species can introduce as a special indicator of mercury and heavy metal levels in the aquatic ecosystem.