Water soluble polymethyl(1-undecylic acidyl)silane was synthesized by the hydrosilylation of 10-undecylenic acid with polymethylsilane catalyzed by 2,20-azobisisbutyronitrile. The arc-discharged SWNTs were ultrasonically dispersed in an aqueous solution of polymethyl(1-undecylic acidyl)silane and then subjected to ultracentrifugation. Raman spectroscopic characterization confirmed that  the supernatant is enriched in the metallic SWNTs, especially those with chiral indexes of (14,2), (15,0), (13,1), (12,3) and (19,1) metallic SWNTs. In this work, the SWNTs of larger diameters and smaller chiral angles than those reported previously were selectively extracted. Moreover, FT-IR spectroscopy and Raman scattering evidence the charge transfer between polymethyl(1-undecylic acidyl)silane and SWNTs. It is assumed that polymethyl(1-undecylic acidyl) silane could wrap chiral-index-selectively onto SWNTs through a fairly weak CH–p interaction, and that the stiffness and length of main chains and side chains as well as the charge state of the polymethylsilane derivative play vital roles in the selective extraction of metallic SWNTs.