AM1 calculations are performed to study the non-linear optical (NLO) properties of push-pull quinones. The variations of molecular structure, linear (a) and NLO polarizabilities (b, c) for a set of push-pull quinones are discussed in terms of quinoid-benzenoid character (QBC), and the strength of donor-acceptor pairs The parameter already used for the polyene (dDA). dDA, bridge, is still valid in rationalizing the donor»acceptor strength for quinoid derivatives. In addition, we examined how an external electric-eld created by ìSparklesœ in the MOPAC package drives a quinoid molecule from the quinoid limit to the benzenoid limit, and how it aÜects the NLO properties. The results show that the eÜect produced by Sparkles is qualitatively similar to that of donor»acceptor pairs.