A novel polysiloxane bearing (N,N)-dimethyl-γ-aminopropyl-γ-aminopropyl side groups(ASO-2) was synthesized by copolymerization of octamethylcyclotetrasiloxane with (N,N)-dimethyl-γ-aminopropyl-γ-aminopropyl methyl dimethoxysilane and hexamethyldisiloxane. Chemical structure, film morphology and the softening fabric property of ASO-2 were characterized and investigated by IR, 1H-NMR, SEM, atomic force microscope(AFM) and Kawabata evaluation system(KES).The experiment results indicate that ASO-2 can form a hydrophobic film on both the cotton fiber and silicon wafer surface. The ASO-2 film relatively exhibits a non-homogeneous structure and uneven morphology in its AFM images. Consequently, in 2 μm2 scanning field, the root mean square roughness of ASO-2 film reaches to 0.226 nm, which is 2.69 times rougher as compared with that of N-β-aminoethyl-γ-aminopropyl polysiloxane (ASO-1) film. Application experiments indicate though the tactile of ASO-2 imparted on 100% cotton is somewhat rougher than that of ASO-1, the whiteness and wettability of the cotton treated by ASO-2 are better than those by ASO-1.