This paper presents the results of a series of cyclic triaxial tests carried out on sands with different index properties. Samples from three grain-size distributions of Izmir (Turkey) sand were tested under consolidated-undrained conditions. The tests were performed under two different effective confining pressure values (100 and 200 kPa). The relative densities of the specimens were 30 and 50%. The results showed that the relative density plays a dominant role in the liquefaction behavior of the sand, whereas the confining pressure increase has greater effects on the stress-strain properties of the sand. It was observed that the relationship between the grain-size diameters and cyclic stress ratios of the sands would be more realistic. It was found that the pore water pressure generation curve falls outside the narrow band proposed by previous studies and a greater coefficient is required for the cycle ratio depending on the soil properties and test conditions. The shear moduli of the sands increased independently of the mean diameter with the relative density under a confining pressure of 100 kPa. Under a confining pressure of 200 kPa, the shear moduli increased with the uniformity coefficient of the sand. Increments in the relative density resulted in a slight increment of the shear moduli for the sands. The goal of the current study was to provide an understanding of the liquefaction and stress-strain behavior of Izmir sand, which represents the material of similar sites with loose alluvial sediments located in earthquake-prone areas found around the world.