A characterization of poly[( l-trimethylsilyl)-1-propyne] (PTMSP) membranes treated with chlorine water is presented. PTMSP chlorination was carried out by dipping a PTMSP membrane in chlorine water at 25 degrees C. X-ray microanalysis reveals that after treatment the chlorine amount is relevant in the whole section of membranes and that the chlorine concentration increase is balanced by the silicon concentration decrease. Pristine PTMSP and chlorinated PMSTP vibrational spectra allow to suppose that in the macromolecule "special sites" are present which may be preferentially attacked by chlorine. A chlorination reaction scheme is given here.