On the basis of ZINDO program, we have desig ned aprogram to calculate the nonlinear seco nd-order polarizabilit iesβijβk andβu according to the SOS equation. The second-order nonlinear optical properties of diazadistyrene derivatives were studied. The calculated result s reveal that the introduction of py rimidine does not inf luence the transpar ency but givea rise to large values of β. For the corresponding stilbene derivatives, the effect of the location of py rimidine on the values of βis greater.