PURPOSE: To obtain an org. nonlinear optical material having a large nonlinear optical effect and excellent formability by using coplymers consisting of specified structural units.

CONSTITUTION: This material consists of copolymers having structural units expressed by formulae I-III, containing 0-100mol% of the unit of formula I, 0-50mol% of the unit of formula II, and 0-50mol% of unit of formula III, and having 10000-2000000 mol.wt.. In formula I, (m) is an integer 1-10, (n) is 0 or 1, R1 is a methyl group or phenyl group, X is -NR2-or-O-, R2 is a hydrogen atom or methyl or ethyl group, A is -NO2, -CN, -CF3, etc., Y is expressed by formula IV, and R3 is hydrogen or same group as A. In formula II, R4 is an alkyl group. The copolymer is synthesized in processes of polymn., hydrolysis, formation of acid chloride, and introduction of photofunctional groups.