Advertising constitutes an integral component of social language. By virtue of diverse expressive forms and techniques, it captures consumers’ attention, stimulates their interest, and further motivates them to make purchases of products. To achieve advertising objectives, advertisers employ a wide array of linguistic strategies to persuade or entice people into buying their products or availing themselves of relevant services. In this process, advertising language may exhibit potential deceptiveness, though such a feature does not necessarily result in the deception of consumers. Experts and scholars have conducted extensive analyses of the potential deceptiveness embedded in advertising language from multidisciplinary perspectives, including psychology, sociology, economics, and linguistics. Drawing on the Cooperative Principle proposed by the American linguist H. P. Grice, this study argues that the violation of the Cooperative Principle in advertising language constitutes a crucial source of its potential deceptiveness. Adopting a qualitative case study approach, this paper primarily explores potentially deceptive language in English advertisements from the vantage point of the Cooperative Principle. It conducts an in-depth analysis of the linguistic characteristics, expressive forms, rhetorical devices, lexical choices, and syntactic structures of such potentially deceptive language in English advertisements. The ultimate aim is to enhance consumers’ understanding of English advertisements and provide effective guidance for them to identify potentially deceptive advertisements and improve their self-protection capabilities.