The unbound granule material (UGM) is widely applied as the base/subbase layer in pavement engineering. The poor quality of UGMs mainly result in differential settlement and fatigue failure of UGMs. This paper presents a laboratory investigation on the influence of the maximum particle size (MPS) of aggregates on the resilient modulus (MR) of UGMs. The repeated load triaxial tests were performed under different stress levels. Three nonlinear models were compared to describe the mechanical behavior of UGMs. The results show that the particle size plays a significant role in the MR of UGMs. When the MPS of UGMs increases from 19mm to 26.5mm, its dynamic MR increases by 6.8% on average. When the particle size increases from 26.5mm to 31.5mm, the dynamic MR increases by 13.3% on average. Meanwhile, the MR is also dependent on the deviatory stress and the confining pressure. The N37A model has a better goodness of fit than the others. In a word, it effects of the MPS should be taken into account in the pavement design, to make sure that the loading and deformation of pavement structure more uniform.