The measurement of concentration in colloidal silica nanoparticles and quartz nanocrystals dispersions by using an optical fiber reflectometer is reported. The reflected light intensities assessed by the fiber sensor were applied on the computation of autocorrelation functions, and the decay rates were associated to the colloids concentrations. The sensor provided reliable results, with sensitivities of 0.45 wt% ms and 0.23 wt% ms on the analysis of quartz and silica dispersions, respectively, for concentrations <1wt%. The differences on decay rate profiles are probably due to the differences on particles morphology and average dimension, as observed in the scanning electron microscopy images. Ver menos