This paper presents a precise study of second-order optical nonlinearity of uniaxially cold-drawn and poled ferroelectric Nylon 11 films. The effects of drawing and poling on refractive indices and second-order nonlinear optical coefficients have been investigated. Drawing caused increase of refractive index (n) parallel to the drawing direction n(X), and decrease of n perpendicular to drawing direction in the plane of film n(Y), as well as decrease of n on the poling direction parallel to film thickness direction n(Z). Poling caused significant increase of n(Z) and decrease of n(Y). These n results imply that poling aligns the molecular chains so that carbonyl groups in Nylon backbone orient in the poling direction (Z-axis). Cold-drawn and poled Nylon 11 films belong to the mm2 point group. Dependence of second-order harmonic generation (SHG) intensity on incidence angle, i.e., Maker fringe pattern, could be precisely fitted using five independent nonzero:tensor components, d(33), d(32), d(31), d(15), and d(24). However, Kleinman symmetry was not satisfied: d(31) not equal d(15) and d(32) not equal d(24). The tensor components d(33), d(31), d(15), and d(24) increase with increasing remanent polarization, whereas the value of d(32) was negligibly small irrespective of the intensity of the remanent polarization. Tensor components of microscopic first-order hyperpolarizability, beta(zxx), beta(zyy), beta(zzz), beta(xxz), and beta(yyz) Were determined. Tensor component beta(zzz) was the largest and beta(zxx) had negative Sign. Second-order nonlinearity was largely suppressed in the vicinity of the melting point of Nylon Il.