The experimental results for the nonresonant third order nonlinearity of the polymer films doped with acceptor donor azobenzene derivatives are reported. Comparison of both third order nonlinearity of the samples and the molecular structure of azobenzene derivatives are performed. It is found that a larger third order nonlinearity corresponds to a stronger acceptor and donor electron capability in the molecules, and attaching the side group to the benzene ring may increase the molecular dipole moment, hence the third-order nonlinear susceptibility. Tt is demonstrated that third-order nonlinearity of the samples is produced mainly from molecular reorientation of photoinduced cis-trans isomerization.