Nylon 66 copolymers were prepared by melt polycondensation of nylon 66 salt with 10-30 mol% (in feed) of 1,3-propanediol and 2,2-dialkyl-1,3-propanediols, where the alkyl groups are dimethyl, diethyl and butylethyl. Reduced specific viscosity was decreased by the copolymerization. Comonomer contents in copolymers were considerably smaller than those in the feed. Crystallinities and densities of melt-pressed films as well as heat-treated films decreased with increasing content of comonomer and length of alkyl side chain in the comonomer. Glass transition temperature and melting temperature were decreased by the copolymerization, and an increase in the length of the alkyl side chain reduced the melting-temperature depression of heat-treated films. Dye uptake and thermal shrinkage were increased and alkali resistance, water absorption and Young’s modulus were decreased by the incorporation of comonomer having an alkyl side chain. These results are discussed and compared with those for the previously reported poly(ethylene terephthalate) copolymers.