Silicon atom substituted new PPV derivatives, poly(2-trimethylsilyl-1,4-phenylenevinylene) (TMS-PPV) and poly[2,5-bis(trimethylsilyl)-1,4-phenylenevinylene] (BTMS-PPV) were synthesized through water-soluble precursor route. The third-order nonlinear optical susceptibilities, chi((3)) (-3 omega;omega,omega,omega), were determined by third-harmonic generation measurement technique at 1907 nm,fundamental wavelength. The measured chi((3)) values of PPV, TMS-PPV and BTMS-PPV were 3 x 10(-12) esu, 3 x 10(-12) esu and 4 x 10(-12) esu, respectively.