Abstract: It is very important to develop accurate methods for the determination of trace mercury due to its extremely hazardous and bioconcentration effect on human health and the environment. The conventional detection methods for Hg(Ⅱ), such as Atomic Spectrometry, Inductively Coupled Plasma-Mass Spectrometry, Electrochemical Analysis and Spectrophotometry, require complex sample preparation, expensive instruments, and lengthy analysis, which cannot meet the needs of the actual analysis. The colorimetric method has been widely applied for detecting Hg(Ⅱ), but the sensitivity and selectivity are still difficult to measure trace Hg(Ⅱ) in a complex matrix. In recent years, nanomaterials of gold (Au) or silver (Ag) have attracted the attention of many researchers in the application of colorimetric detection for Hg(Ⅱ) because of their unique surface plasmon resonance, and many new methods have been successfully applied to detecting trace Hg(Ⅱ) in actual samples. The main colorimetric detection mechanism of Au/Ag nanomaterials is based on the fact that Hg(Ⅱ) could cause the aggregation/redispersion or the redox reaction, which induces a color change in the solution. This method has been applied successfully to water samples, however, large interferences exist for other kinds of samples. In this paper, the theory and research progress of Au and Ag nanomaterials in the colorimetric detection of Hg(Ⅱ) are reviewed. This is a new direction for establishing a simple, rapid, highly sensitive and highly selective colorimetric detection method for trace Hg(Ⅱ) measurements in complex samples in the future.