Abstract: To investigate the effect of maximum aggregate sizes (MAS) on the uniaxial tensile failure mode, nominal tensile strength and corresponding size effect of double-edge notched concrete specimens, a meso-mechanical numerical model based on the continuous grading random aggregate model was established from the mesoscopic perspective. It indicated that under the same structural size, the nominal tensile strength increases and the size effect is gradually weakened with increasing MAS. Moreover, based on the Type-2 size effect law, a theoretical size effect law considering the effect of MAS on the nominal tensile strength was proposed and verified. The theoretical size effect law can quantitatively predict the size effect behavior on tensile strength based on known physical parameters (i.e., structural size D and MAS d_max).