The behavior of soil-geosynthetics interfaces depends on the different properties of soil, including particle size, particle shape, density, gravimetric water content, degree of saturation, and properties of geosynthetics that include structure, texture, and other elements. This paper pertains to the study of the influence of the particle shape of sand on the behavior of the sand-geotextile interface. Experiments were conducted using a conventional-sized direct shear box modified for interface testing. In the present study, two different natural sands (one with angular particles and the other with rounded particles) and two different geotextiles were used. The results showed that particle shape significantly influences the interface behavior, especially the postpeak behavior. (C) 2013 American Society of Civil Engineers.