Two series of new thermoplastic poly(thiourethane-urethane) elastomers (EPTURs), with different hard-segment content (40–60 wt%), were synthesized by a one-step melt polymerization from poly(oxytetramethylene) diol (PTMO) of \( \overline{M}_{\text{n}} \) = 1,000 g mol⁻¹ or poly(hexamethylene carbonate) diol (PHCD) of \( \overline{M}_{\text{n}} \) = 860 g mol⁻¹ as a soft segment, hexane-1,6-diyl diisocyanate and (methylenedi-1,4-phenylene)dimethanethiol as a chain extender at the NCO/(OH + SH) molar ratio of 1. The structures of all the EPTURs were examined by Fourier transform infrared spectroscopy (FTIR), atomic force microscopy and X-ray diffraction analysis. Their thermal behavior was investigated by means of differential scanning calorimetry and thermogravimetric analysis (TG). For the chosen polymers the gaseous products evolved during the decomposition process were analyzed by TG-FTIR. Moreover, physicochemical, adhesive and tensile properties as well as Shore A/D hardness were determined. The resulting high-molecular-mass EPTURs were stable up to 254–262 °C, as measured by the temperature of 1 % mass loss. They decomposed in three or four stages. The main decomposition products were carbonyl sulfide, isocyanate, carbon dioxide, aromatic hydrocarbons as well as aliphatic ethers and aldehydes (in PTMO series) and alcohols (in PHCD series). All the polymers showed partially crystalline structures, associated with crystallization of thiourethane hard segments. Their melting temperatures were in the range of 184–186 °C. The PTMO series EPTURs exhibited better low-temperature properties (glass-transition temperature in the range of −64 to −44 vs. −26 to −22 °C), but poorer tensile strengths (20–28 vs. 37–43 MPa). These EPTURs showed improved adhesive properties in comparison with their polyurethane analogs.