PURPOSE: To obtain the subject new compound suitable for practical organic nonlinear optical elements having great nonlinear optical effect, excellent in chemical and thermal stability and transparency, easy to grow crystals from solution or melt phase, and easy in processing.

CONSTITUTION: This cyclobutendione derivative is expressed by formula I [X1 is a halogen; X2-X5 are each H or a halogen; R is of formula II (C* is an asymmetric carbon atom)], e.g. 1-chloro-2-(4-fluorophenyl)-cyclobuten-3,4-dione. The compound of formula I is obtained by reaction between a new cyclobutendione derivative of formula III (Y is Cl, Br, methoxy or ethoxy) and asymmetric 1-amino-2-propanol of formula IV. This compound of formula I is excellent in heat resistance, weatherability, transparency, durability and processability.