Wilson's disease is a treatable autosomal recessive inherited disorder of copper metabolism due to mutation of the copper transporting gene. The basic strategy of treatment is to reduce the amount of copper in the liver and other tissues by administering both a low copper diet and copper-chelating agents. D-penicillamine is the first choice as a copper-chelating agent. Some serious side effects could occur in 3~5% of all patients following D-penicillamine therapy. We report a 19 year-old male with Wilson's disease who developed nephrotic syndrome 6 months after the initiation of D-penicillamine therapy. Prednisolone was administered to control nephrotic syndrome and D-penicillamine was switched to trientine. Urinary remission was achieved within a week and maintained thereafter. Nephrotic syndrome was proven to be MCNS by kidney biopsy.