Second‐order nonlinear optical properties of a newly synthesized dye‐attached polymer (3R) were investigated. The dye has a conjugated diazo structure, and the &bgr;&mgr;g(&bgr;: second‐order molecular hyperpolarizability, &mgr;g: dipole moment in the ground state) is larger than five times that of a monoazo dye (2R). The second‐order nonlinear coefficient (&khgr;(2)) of a 3R polymer is also greater than that of a 2R polymer throughout the fundamental wavelength of 1.06 &mgr;m and between from 1.50 to 1.70 &mgr;m when the polymers are electrically poled. For both polymers, the &khgr;(2)dependence on the fundamental wavelength corresponds to the absorption spectrum, which is explained by two‐photon resonance near the absorption maxima. The attainable &khgr;(2)of the polymers deviates from the theoretical linear relationship with the dye content when it is high. This indicates that the dipolar interaction increases as the dye content rises.