Natural pozzolanas should be evaluated in terms of sustainability as well as their contribution to concrete durability. Therefore, the use of such materials in the production of cement as well as concrete industry has been gaining importance recently. In this study, the pozzolanic activities of ground trachyte and rhyolite, known as volcanic tuffs, were investigated in accordance with TS 25 standard. Pozzolanic properties of such materials, along with their pozzolanic activity indices, are investigated comparatively by the Frattini method, strength activity index, X-ray diffraction and thermogravimetric analysis. The morphologies of ground trachyte and rhyolite were also studied using SEM analysis. Based on the results obtained, the mortar samples containing blast furnace slag (BFS), fly ash (FA), trachyte and rhyolite were met the acceptable pozzolanic activity index at the end of 28 days with values of 90, 87, 89, 87, respectively. On the other hand at the end of 90 days, while the mortar samples containing BFS, FA and trachyte were met the acceptable pozzolanic activity index, that of containing rhyolite did not meet the acceptable pozzolanic activity index, with values of 93, 85, 87, 80, respectively. The pozzolanic activity index of the rhyolite was found to be quite close to that of the FA; however, the trachyte had a pozzolanic activity index close to the BFS. Comparisons of the methods implemented in the analyses were also conducted. According to the statistical evaluation of the test methods, it has been found that the relationships obtained using the direct methods as well as the indirect methods independently are highly correlated. Overall, it can be concluded that the ground trachyte may be utilized as a pozzolanas in the cement industry; however, the ground rhyolite does not meet some limits prescribed by the related standard.