Background. The clinical presentation of mercury (Hg) intoxication may mimic rheumatic diseases. Hg exposure is associated with systemic lupus erythematosus (SLE)-like disease in genetically susceptible rodents and Hg is among the environmental factors in the development of SLE in humans. Herein, we presented a case with clinical and immunological features suggestive of SLE but diagnosed with Hg intoxication. Case. A thirteen-year-old female with myalgia, weight loss, hypertension and proteinuria was referred to our clinic for the evaluation of possible SLE. Physical examination of the patient was unremarkable except for a cachectic appearance and hypertension, laboratory investigation revealed positive anti-nuclear antibody, dsDNA antibody and hypocomplementemia with nephrotic range proteinuria. Inquiry for toxic exposures revealed a continuous exposure to an unknown silverly shiny liquid for a month which was thought to be Hg. Due to the fulfillment of Systemic Lupus International Collaborating Clinics (SLICC) classification criteria for SLE, a percutaneous kidney biopsy was performed whether proteinuria resulted because of the Hg exposure or flare of lupus nephritis. Blood and 24-hour urine Hg levels were high, and no findings associated with SLE were observed in the examination of the kidney biopsy. The patient was diagnosed with Hg intoxication and, clinical and laboratory findings, including hypocomplementemia, positive ANA and anti-dsDNA antibody, improved with chelation therapy. Also, no findings associated with SLE were observed in the follow-up of the patient. Conclusions. In addition to the toxic effects, Hg exposure may cause autoimmune features. As far as we know, this is the first-time Hg exposure was associated with hypocomplementemia and anti-dsDNA antibody in a patient. Also, this case highlights the inconvenience of the use of classification criteria for diagnostic purposes.