Photochemical isomerization of p,p’-bis(chloromethyl) azobenzene (CAB) was investigated in poly(N,N-dimethyl-4-vinylphenethylamine-block-styrene) block copolymer CP(PTA-b-St)]. The P(PTA-b-St) was prepared by anionic living polymerization. Both ends of CAB were attached to amino groups of the PPTA in the P(PTA-b-St) by quaternization in order to permit cross-linked films. When the films were irradiated with u.v. light (300 nm < lambda(1) < 380 nm), CAB underwent photoisomerization from the trans to the cis form. The photoisomerization did not proceed in a first-order kinetics. Hence, irradiation time dependence of the results was analysed by the Kohlraush-Williams-Watts equation. The resultant values of parameter alpha, trans fraction at equilibrium (C-e) and a half-life period (tau(1/2)), remained constant from 15 degrees C to 30 degrees C, but discontinuously changed at approximately 30 degrees C which is close to the glass transition temperature (T-g) of PPTA. Therefore, the films were first irradiated with u.v. light at 60 degrees C for 2 h, resulting in a 28% content of cis form in CAB. Subsequently, when the films were irradiated with visible light (420 nm < lambda(2)) at 20 degrees C for 2 h and 90 degrees C for 2 h, the cis content of CAB changed to 21% and 0%, respectively. The retention and deletion of the cis form was controlled by an alternation of the thermal motion of PPTA above and below the T-g of PPTA in the P(PTA-b-St) block copolymer.