The results of more than 1000 simulations carried out using the SIMFRAC Programme, on fracture generation in rocks is presented in this paper. A numerical simulation method has been used to predict connectivity of fractured rock masses. In all simulations performed there is a threshold of fracture density, below which fractures are poorly connected with no percolation. Where fracture density is at the Percolation Threshold, a continuous and connected Fracture Cluster is developed starting the percolation of the system. The geometrical configuration of the Critical Fracture Cluster is determined by his fractal dimension, which consequently may be used to measure the connectivity of fractured rock masses