In this paper the dielectric properties of nanosize ferroelectric lead titanate crystals are presented. The PbTiO3 samples were prepared by pressing nanopowder into the plates and have been studied experimentally by dielectric permittivity measurements in a wide frequency and temperature range. The obtained TC dependence shows a critical change of behavior with increasing of mean nanoparticle size in a 9 nm region. The theoretical calculations based on Monte Carlo simulation were performed to describe such behavior of this material. It was shown that taking into account distribution of nanoparticle sizes in sample is possible to describe dielectric properties of PbTiO3 nanocrystals rather well.