Granular-type FePt films with perpendicular magnetic anisotropy are fabricated onto glass substrates by annealing FePt/MgO multilayer films. The uniaxial perpendicular magnetic anisotropy constant (K-u) and the activation volume (V*) are obtained by fitting the remanent coercivity as a function of the applied field waiting time using the Sharrock's formula for oriented magnetic grain assembly. K-u increases with annealing temperature and annealing time, as a result of the enhanced chemical ordering in L1(0) phase FePt grains. V* tends to decrease with annealing time revealing the FePt grain separation process by the MgO matrix with annealing. By modifying the initial FePt/MgO multilayer structure and annealing condition, the optimized FePt-MgO film shows a high K. and a small V* value.