In this article, a soluble poly[2-methoxy-5-(3'-methyl) butoxy]-p-phenylene vinylene (MMB-PPV) was synthesized by dehydrochlorination reaction and the MMB-PPV film was implanted by nitrogen ions (N+) with the ion dose and energy in the range of 3.8 x 10(15) to 9.6 x 10(16) ions/cm(2) and 15-35 keV, respectively. The surface conductivity, optical absorption, optical band gap (E-g) of modified MMB-PPV film were studied, and the third-order nonlinear optical susceptibility (chi((3))) as well as its environmental stability of modified MMB-PPV film were also measured by degenerate four-wave mixing system. The results showed that the surface conductivity of MMB-PPV film was up to 3.2 x 10(-2) S when ion implantation was performed with the energy of 35 keV at an ion dose of 9.6 x 10(16) ions/cm(2), which was seven order of magnitude higher than that of the pristine film. UV-Vis absorption spectra demonstrated that the optical absorption of MMB-PPV film was enhanced gradually in the visible region followed by a red shift of optical absorption threshold and the E-g value was reduced from 2.12 eV to 1.59 eV with the increase of ion dose and energy. The maximum chi((3)) value of 2.45 x 10(-8) esu for modified MMB-PPV film was obtained with the ion energy of 20 keV at an ion dose of 3.8 x 10(16) ions/cm(2), which was almost 33 times larger than that for pristine film. In comparison to the reduction of 17% in the chi((3)) value of pristine MMB-PPV film, the maximum chi((3)) value of 2.45 x 10(-8) esu for modified MMB-PPV film decreased by over 5.3% when they had been exposed under the same ambient conditions for 90 days. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2072-2077, 2010