Poly(diallyldimethyl ammonium chloride-vinyl trimethoxysilane) [P(DADMAC-VTMS)l and poly(diallyldimethyl ammonium chloride-acrylamide-vinyl trimethoxysilane) [P(DADMAC-AM-VTMS)1, the latter a new cationically charged and hydrophobically modified flocculant, were obtained by radical polymerization initiated by potassium persulfate. The effects of the vinyl trimethoxysilane (VTMS) feed ratio on the intrinsic viscosity and solubility of the polymers were examined. The effects of the flocculants on turbidity removal, decolorization, and oil removal in water treatment were also studied. The introduction of VTMS increased the intrinsic viscosities of P(DADMAC-VTMS) and P(DADMAC-AM-VTMS) in comparison with the viscosities of poly(diallyldimethyl ammonium chloride) and poly(diallyldimethyl ammonium chloride-acrylamide), respectively, but reduced their solubilities. The introduction of VTMS also enhanced the flocculation properties of P(DADMAC-VTMS) and P(DADMAC-AM-VTMS), including turbidity removal, decolorization, and oil removal.