Flocculation and settlement of fine sediments play an important role in silt transportation, soil penetrability and pollutant translocation in the Three-Gorges Reservoir. Surface charge properties of fine particles of the purplish soil in the Three Gorges Reservoir Region were determined and effects of Mg²⁺ and K⁺ on deposition of fine sediments in static water were studied with the pipette technique. Results show that (1) the surface potential of the fine particles of acidic, neutral, and calcareous purplish soils was -0.156, -0.171 and -0.192 V, respectively, in the 2:1-type electrolyte system, and varied in the range of -0.310~0.390 V in the 1:1-type electrolyte system; (2) when the concentration of Mg²⁺ and K⁺ was 0.1 mol m^-3 in the systems, settling velocity of the silts of the three different purplish soils reached 1.56 cm min^-1, 1.47 cm min^-1, and 1.35 cm min^-1and 1.05 cm min^-1, 1.01 cm min^-1 and 0.99 cm min^-1, respectively, showing that the higher the surface potential, the lower the settling velocity; and (3) the mean settling velocity of the fine silts of the three purplish soils increased with the concentration of the electrolyte of the Mg²⁺ and Na⁺ ystems. Besides, a concentration threshold was observed in either Mg²⁺ or K⁺ system for flocculation and settlement of fine silts, being about 0.1 mol m^-3 in the 2:1-type electrolyte system and 0.25 mol m^-3 in the 1:1-type electrolyte system.