This article describes the syntheses and second-order nonlinear optical (NLO) properties of novel types of polyesters containing second-order NLO active chromophores with high density, which were obtained by condensation polymerization using two comonomers with the N,N-dialkyl-4-nitroaniline or N,N-dialkyl-4-((4-cyanophenyl)azo)anilin moiety. The polyesters were synthesized by condensation polymerization between isophthalic acid derivatives and N-substituted diethanolamines using triphenylphosphine and diethyl azodicarboxylate as the condensation reagents in dimethyl sulfoxide (DMSO) or 1-methyl-2-pyrrolidinone (NMP). The obtained amorphous polyesters exhibited good solubility in common organic solvents and provided optical-quality films by spin-coating. The SHG measurements of the spin-coated films of the resulting polyesters were carried out by the Maker fringe method using a Q-switched Nd:YAG laser (1064 nm) as an exciting beam after corona-poling. One of the polyesters, which was prepared from 5-[2-(N-methyl-4-nitroanilino)ethoxy]isophthalic acid and N-[4-((4-cyanophenyl)azo)phenyl]diethanolamine, exhibited the large second-order NLO coefficient, d(33), of 202 pm/V. On the other hand, a polyester containing chromophore moieties with the highest density, which was prepared from 5-{[1,3-bis[4-((4-cyanophenyl)azo)-N-methylanilino]-2-propyl]oxy}isophthalic acid and N-[4-((4-cyanophenyl)azo)phenyl]diethanolamine, exhibited good temporal stability of the second-order nonlinearity at ambient temperature.