Abstract: A colloidal shear thickening fluid(STF) was generated by dispersing self-made SiO₂ particles with different size in 200 molecular weight polyethylene glycol(PEG200) using the ball-milling technique. The STF/Kevlar composites were prepared by the static impregnation method. The effect of particle size on the rheological behavior of the fluid systems and the stab resistant properties of STF/Kevlar composites were studied. The results show that the suspensions with different SiO₂ particle sizes all have notable shear thickening behavior. Under the condition of the same SiO₂ mass fraction, the initial viscosity, critical shear rate and highest viscosity of fluid system decrease as the particle size increasing. 16-layer STF/Kevlar targets provide protection without penetration against spike at the impacted energy of 24.0 J, which are significantly better than that of the pure Kevlar with equal areal density. As the particle size increases, the composite targets have better stab resistance against spike. Under the impacted energy of 13.0 J, the STF/Kevlar targets exhibit better stab resistance against knife than that of the pure Kevlar target with equal areal density. As the particle size increases, the depth of penetration into the backing material decreases. Shear fracture is the main damage form of the targets.