Growth of Pt nanocrystals has been investigated by means of electron beam evaporation of Pt layer and post rapid thermal annealing. The results indicate that the density of nanocrystals increases first with the annealing temperature and the annealing time，followed by a slight decrease. Uniformly distributed nanocystals with a density of 30×1011 cm-2 can be obtained in the case of the annealing at 800℃ for 20 s. Further，memory effect of Al2O3/Pt nanocrystals/HfO2-based MOS capacitors has been characterized，indicating a capacitance-voltage （C-V） hysteresis window as large as 201 V in the sweep voltage range of -3—+8 V. In terms of the same programming time，the flat band voltage shift of the memory capacitor starts to increase remarkably when the programming voltage is increased to 9 V. This is related to a decrease in the energy barrier across the tunneling layer for electrons，i.e.，the tunnel mechanism of electrons is changed from direct tunneling to Fowler-Nordheim tunneling. Moreover，the memory capacitor also exhibits a capability of continuous electron trapping with prolonging of the programming duration.