PbS nanocrystallites with a diameter smaller than 15 nm doped in silica aerogel matrix have been prepared by sol-gel route preceding supercritical drying technique and colloidal chemistry method. These PbS-nanocrystals-doped aerogels were characterized by optical absorption, X-ray diffraction (XRD) and transmission electron microscopy (TEM). Blue shifts in optical absorption threshold indicate that the PbS crystallite sizes range from 5 to 15nm with an increase of annealing temperature from 298 to 1023 K. It has been speculated that three mechanisms exist during the growth of the PbS nanocrystallites, and various apparent growth excitation energies were calculated using an Arrhenius relation.