Natural sands may lead to alkali-silica reaction in concrete when the conditions are favorable. However, natural sands vary in composition and therefore may demonstrate different reaction characteristics. The aim of this study is to compare alkali-silica reactivity of seven different natural sands with different origin. The particle size distributions for sand samples were firstly obtained by sieving method. Petrographic examinations, mineralogical and chemical analyses were firstly conducted to determine the mineralogical and chemical composition of sands. Then, accelerated mortar bar tests, ASTM C 1260, were performed. Additionally, SEM observations were conducted on the mortar bars. According to the results obtained, sands containing active silica and silicate minerals, metamorphic and volcanic rock particles are found to be potentially dangerous for alkali-silica reaction (ASR). The SEM observations have supported the expansion data. (C) 2011 Elsevier Ltd. All rights reserved.