Numerous researches have been focusing on the roles of fines in liquefaction resistance of sand matrix soils (sand dominant soil that contains little presenting fines). It has been reported that the presence of plastic fines would either imposed additional liquefaction resistance of sand matrix soils or caused reduction to the liquefaction resistance. This paper aims to present the liquefaction resistance of sand matrix soils with respect to different fines content based on the results from cyclic tests using triaxial testing system. The sand matrix soils were reconstituted by mixing the plastic fines (kaolin and bentonite) to the clean sand at seven different percentages by weight. Results showed that liquefaction resistance of sand matrix soils decreases with an increase of fines content until a minimal value and increases thereafter. It was identified that the presence of fine contents to give the minimum liquefaction resistance were 20 % for sand-bentonite mixtures and 25 % for sand-kaolin mixtures. These values represent the threshold fines content for respective mixtures.
