From a Chinese chemical regulatory perspective mixtures are categories of substances which are different from mono-constituent substances. There is no clear division of substance types described both in Measures on the Environmental Management of New Chemical Substance (hereinafter referred to as “Measures”) and New Chemical Substance Notification Guidance Document (hereinafter referred to as “Guidance”). Whereas, “Substance Type” in Part III of the application form are classified into three types, namely substance with unique molecular structure, substance without unique molecular structure and Polymers. Undoubtedly, mixture falls into the category of substance without unique molecular structure. In practice, to help choose appropriate notification strategy and testing method, we divide the mixtures into two groups, the multi-constituent substances and UVCB substances according to the Guidance for Identification and Naming of Substances under REACH and CLP.