Poly[(4-nitronaphthyl)[4-[[2-(methacryloyloxy)ethyl]ethylamino]phenyl]diazene] (pNDR1M) was prepared. The effect of the size of the azo moiety in the optical storage properties was studied. Both writing and relaxation processes can be described by biexponential functions. The bulkier pNDR1M exhibits a slower writing rate. However, there is no significant difference in the maximum birefringence achieved and in the relaxation rate when compared with the less bulky poly[(4-nitrophenyl)[4-[[2-(methacryloyoxy)ethyl]ethylamino] phenyl]diazene] (pDR1M).