Chert, which is a crypto and/or microcrystalline sedimentary rock, may lead to alkali-silica reaction in concrete when the conditions are favorable. However, cherts vary in composition and consequently may demonstrate different reaction characteristic. In this study, eight different chert types were investigated. Accelerated mortar bar test, ASTM C 1260, was performed on aggregate blends of limestone and chert. Ten sets of mortar bars with varying amount of cherts, 1 to 100%, were tested for each chert type. Additionally, sonic velocity measurement and petrographic examination were conducted on the mortar bars. The mortar bar test revealed that all cherts show pessimum behavior with maximum expansion peak attained in the range of 5-15% chert content: the expansion due to the alkali-silica reaction increases up to pessimum content and decreases thereafter. The sonic velocity measurements and the petrographic examinations have supported the expansion data that the minimum velocity and the maximum cracking occur in the peak expansion range. The different testing methods have complemented each other that the pessimum content for all the cherts investigated was found to be 7.5-10%. (C) 2007 Elsevier Ltd. All rights reserved.