Abstract: Due to few experimental achievements on scale effect of mechanical properties of rockfill materials, series of triaxial tests are made with different gradations and maximum diameters. The maximum diameters are 20, 40 and 60 mm. The 9 groups of gradations are designed with the same fractal dimensions under differecnt maximum diameters. The values of fractal dimensions are 2.3, 2.6 and 2.7, respectively, which represents coarse materials, medial materials and fine materials. The sample preparation standard is designed under the same relative density. The results show that the internal friction angles, initial tangent moduli and bulk moduli increase with the increase of the maximum diameters.