Currently numerous manufacturers offer herbal infusions or dietary supplements based on the plant Cistus incanus. These products are especially promoted as offering a high content of phenolic substances together with an associated strong antioxidant activity. For the customers it is of interest, if the advertised phenolic contents are valid, plant material is authentic and if the suggested effects can be obtained through ingestion. As it is known from the literature, phenolic compounds can undergo severe changes resulting from cooking. Therefore, it is important to consider processing parameters such as brewing water, brewing temperature, and brewing duration for the preparation of C. incanus herbal infusions. The aims of this study were to analyze the phenolic compounds of C. incanus herbal infusions, to estimate the antioxidant capacity of the individual phenolic substances, as well as to investigate the influence of the brewing process on the phenolic compound profile. By the use of LC–DAD/ESI–MS/MS thirty-two phenolic compounds (e.g. phenolic acids, flavan-3-ol monomers and -dimers as well as flavonol glycosides) were identified. Additionally, specific antioxidant capacities were attributed to corresponding substances by using the LC–onlineTEAC (Trolox Equivalent Antioxidant Capacity) methodology. Moreover, the selection of brewing water, boiling time as well as boiling temperature had a significant influence on the content of the phenolic compounds in C. incanus infusions. On the basis of these results, it can be concluded, that an incorrect choice of brewing process parameters could result in a decreased amount of phenolic substances in the final C. incanus beverages accompanied with a reduced antioxidant activity.