At Northeast of Turkey, it is possible to find plenty of volcanic origin rocks and rich natural pozzolan beds. In this study, the pozzolanic activities of six types of different tuff samples taken from Trabzon and Bayburt regions (Northeast of Turkey) were examined according to the related standard and it was determined that the compressive strengths were varying between 6.7-11.0 MPa. In addition, the chemical compositions of these samples, except one, were consistent with the related standard. On the other hand, the results obtained from these studies were that increase in the proportion Of SiO2 in the pozzolan increases the pozzolanic activity. (c) 2006 Elsevier Ltd. All rights reserved.