Dielectric relaxation measurements were performed on a series of poly(di-n-alkylitaconate)s with various side-chain lengths. The experimental data were analyzed by adjustment with one or the sum of several Havriliak-Negami functions. They demonstrated the existence of several relaxation processes with significant dielectric relaxation strengths. The comparison of the results obtained by increasing the length of the side groups permitted an assignment of the gamma, beta(fast), and beta(slow) secondary relaxations to motions of the alkyl side chains, ester group located after the CH2 unit, and ester group directly attached to the main chain, respectively. In poly(di-n-alkylitaconate)s with six carbon atoms at least in the alkyl part, the existence of an additional low-temperature glass transition alpha L was clearly established. The alpha(L)-process replaces the beta(fast)-process observed in the lower derivatives. It is located in quite the same temperature and frequency ranges and exhibits a non-Arrhenius behavior. It is likely related to cooperative motions of the alkyl side chains and ester group next to the CH2 spacer unit.