Clay has wide application in engineered barriers, such as buffer barriers in deep geological nuclear waste disposal, clay liners in landfill, and earthen slopes and embankments, to name a few. However, most clay soils have a high potential to crack under extreme weather induced moisture loss. From a macro-mechanical view, clay tensile strength which is a critical factor governing the cracking behavior is highly dependent on the moisture content and corresponding matric suction. In this study, a series of laboratory tests on two typical clays (kaolinite and sodium bentonite) were carried out to investigate the relationship between clay tensile strength and moisture content by using a specially designed device which can measure tensile strength directly (Stirling et al. 2014, 2015). In addition, the study also investigated the effect of silica sand additive on the tensile strength at a wide range of moisture contents. The results demonstrate that both moisture content and sand additive have a significant impact on the measured tensile strength of the clays.