Due to their interesting properties, zwitterionic polymers have been extensively studied; however, only a few reports discuss their thermal degradation. The objective of this work was to study the pattern of thermal degradation of three poly(sulfobetaines) with different lateral chain lengths and the relationship between structure and degradation mechanism of the polymers. Because the initial decomposition temperatures are not significantly different in polymers with different ethylene glycol residues, it was possible to study the thermal behavior of these polymers at the same temperature range. The apparent activation energies of the degradation for polymers, calculated by the Ozawa method, was different for each poly(sulfobetaine). A decomposition mechanism is suggested, which included a Hoffman elimination of the quaternary amine giving vinyl ethers, which in turn, decompose to carboxylic acids, which can suffer and intramolecular cyclization reaction, and finally produce a polypropylene like chain.