The synthesis and characterization of polyisoprene bearing carboxylatobetaines of various intercharge lengths, either at one or at both ends of the polymer chain, are described. Peculiar properties such as associative behaviour may be expected due to their original functionalization. These materials are prepared by anionic polymerization of isoprene and deactivation with dimethylaminopropyl chloride, followed by reaction with bromoalkyl ethyl carboxylic esters and subsequent hydrolysis. Highly viscous solutions are obtained when the polymers are dissolved in solvents of low polarity. Average aggregation numbers are calculated from the viscosity results, which depend on the molecular weight of the aminated precursor polymer as well as the intercharge length of the zwitterionic groups. The effects of temperature and polar additives are also considered.