Aliphatic polydithiourethanes (PDTUs) were successfully synthesized from diisothiocyanates and dithiols having different values of the carbon atom number. The thermal properties and hydrogen-bonding behavior of PDTUs were studied in detail by using differential scanning calorimetry, thermal gravimetric analysis, temperature dependence nuclear magnetic resonance, Fourier transform infrared-attenuated total reflection, and density functional theory and semiempirical molecular orbital methods. In this work, we demonstrated that the thermal decomposition of PDTUs happened from the cleavage of the C-S bond of the dithiocarbamate moiety in the main chain and also that the active isothiocyanate and thiol groups were reprepared in the terminal of the decomposed polymer (i.e., oligomer). Furthermore, we found that the thermal depolymerization of PDTUs and the repolymerization of dithiourethane oligomers at room temperature proceeded repeatedly a few times.