Advertising is an interesting site of linguistic creation and language contact. Code-mixing in Chinese advertising is a powerful tool by means of which copywriters may create a more effective message and, at the same time, it is also a factor in the construction of social identity. Through the analysis of Chinese advertisements in the PRC and Hong Kong, an overview of the role and functions of Chinese dialects and English in code-mixing practices in provided. Besides serving pragmatic functions, dialects emerge as an important part of Chinese cultural heritage and are able to convey a sense of familiarity and authenticity; in contrast, English may be used in the construction of a modern and global identity. Whereas code-mixing in the PRC is constrained by policies aimed at spreading the standard language and at preserving the purity of the Chinese language, the situation seems quite different in Hong Kong, because of the peculiar linguistic and political situation of this region.