Statement of Problem: The chemical reactions occur at the amalgam surface when exposed to bleaching agents. Mercury ion is released from dental amalg-am when bleached.Purpose: The aim of this in vitro study was to investigate the effect of carbam-ide peroxide (CP) on the release of mercury ion from two types of spherical dental amalgam.Materials and Method: Two commercial brands of dental amalgam, Cinalux and GS-80, were selected. 18 amalgam discs of any brand were prepared in silicon moulds according to the manufacturer's instructions. After 60 minutes, the discs were removed and individually immersed in artificial saliva (AS) for 24 h at 37 0C. Then, the discs of any amalgam were divided into two equal test group (A) and control group (B). Each specimen in the test group was treated in eight-hour cycles with 10% CP. The specimens of the control group was treated in similar cycles with AS. All of the solutions were taken for Hg ion release deter-mination, using cold-vapor atomic absorption mercury analyzer system. The data were analyzed using General Linear Model followed by Repeated Measures ANOVA.Results: The results indicated that the bleaching agent significantly caused more mercury ion to be released into the solutions ( p <0.05) but artificial saliva did not show this effect. The release rate of mercury from the Cinalux during the two weeks of treatment period with 10% CP showed an increase from 11.63 µg/lit in the first day to 228.85µ g/lit in the last day. The release rate from GS-80 showed a decrease from 130.96 µg/lit in the first day to 80.68µ g/lit in the last day.Conclusion: Treatment with %10 carbamide peroxide increased mercury release from dental amalgam in comparison with the artificial saliva. The release of Hg from 2 brands of dental amalgam was in a safe range.