This study determined the geochemical properties of phyllosilicates in the Upper Palaeozoic-Lower Mesozoic metamorphic units outcropping from west to east in the vicinities of Göksun, Afşin and Ekinözü towns in the north of Kahramanmaraş province in the westerly part of the Eastern Taurus mountains. Geochemical examination of phyllosilicates (major and trace elements, stable isotope) was carried out on pure K-micas and illite/K-micas separated from low-medium grade metamorphic samples. According to the main oxide composition of the phyllosilicates, illite/K-micas from the areas of Afşin and Göksun contain higher SiO2 and Al2O3 and lower MgO, Fe2O3, MnO and Na2O compared to those in the area of Ekinözü. The minerals represented by schists in the Ekinözü K-micas are close to having a biotite-celadonite composition while those with phyllites in Afşin and Ekinözü are close to muscovite composition. Chlorites have a trioctahedral composition between chamosite and clinochlor. Illite/K-micas with both trioctahedral and dioctahedral characteristics show a composition between muscovite and biotite (biotite-celadonite, muscovite-phlogopite, muscovite-ferriphengite, muscovite-ferrobiotite, Al-phlogopite-Alannite) in general. In the trace element content of phyllosilicate minerals, transition metals and granitoid elements are at high concentrations while other elements, especially elements with low (LFSE) and high field strength (HFSE), display low concentrations. In the chondrite-normalized trace element content of phyllosilicate minerals, chlorites have higher values compared to K-micas and trioctahedral K-micas show lower values compared to dioctahedral K-micas. Rare earth element (REE) distribution of chlorite and sericite/K-mica minerals is normalised to chondrite and North American Shale Composition (NASC); the dioctahedral K-mica of Afşin region has the highest depletion, while the trioctahedral mica of Ekinözü has the highest enrichment. The oxygen and hydrogen isotope composition of the phyllosilicate minerals show that they are in the hypogene region, which represents high temperature and deep environment conditions. The oxygen and hydrogen isotope values of sericite/K-mica and chlorites indicate that the formation temperatures of these minerals varied between 375 and 500 °C. 40Ar/39Ar radiometric age data for the metamorphic rocks show that the metamorphism developed during the Upper Cretaceous (Santonian-Campanian) in the Afşin and Göksun regions and the Lower-Middle Eocene (Ypresian-Bartonian) periods in the Ekinözü region.