Abstract: The expanded perlite as the internal curing material of the cement mortar is selected, and the influences of the size of expanded perlite particles on the shrinkage and mechanical properties of the mortar are studied. The results show that the early water absorbing capacity of the expanded perlite would reduce and the late water releasing speed would improve with the decrease of the size of perlite particles, so the effect of the size of the perlite particles on the shrinkage of cement mortar is related to the time. The mortar with the perlite particles sizes between 0.425 to 0.250mm has the minimum shrinkage in the initial 45 days. The shrinkage of mortar increases with the reduction of the size of perlite particles in 45 to 60 days. The compressive strength, flexural strength and tensile bonding strength of the mortar increase with the reduction of the size of perlite particles, and the reduction of the size of perlite particles is beneficial to improving the flexibility of the mortar.