The effects of amine donors (a:NH 2 , b:NMe 2 , c:NMePh, d:NPh 2 ) and conjugation length on the molecular hyperpolarizabilities of a series of dipolar molecules have been theoretically investigated by using CPHF/6-31G method. The first hyperpolarizabilities (β) of p-nitrobenzene derivatives increase with the donor in the order, NH 2 < NMe 2 < NMePh < NPh 2 , whereas slightly different order is observed in more conjugated derivatives, i.e., NH 2 < NPh 2 < NΜe 2 < NMePh. The result has been attributed to the extent of charge transfer and torsion angle. Moreover, the results show that "non-traditional" π-conjugation effect exists in small compounds and decreases as the conjugation length between donor and acceptor increases.