Abstract: Abstract This paper deals with the size effects of mechanical properties of rockmasses. A mechanical description of the REV related to the elastic modulus of jointed rockmasses is proposed, and an expression of the REV based on the central limit theorem is suggested. The study shows that the REV can be used to reflect the size effect of mechanical properties of rockmasses. The result obtained in this work can provide a new way how to appropriately select the mechanical parameters of jointed rockmasses.