TPDex, a putative dextranase from Thermoanaerobacter pseudethanolicus, was purified as a single 70 kDa band of 7.37 U/mg. Its optimum pH was 5.2 and the enzyme was stable between pH 3.1 and 8.5 at $70^{circ}C$. A half-life comparison showed that TPDex was stable for 7.4 h at $70^{circ}C$, whereas Chaetominum dextranase (CEDex), currently used as a dextranase for sugar milling, was stable at $55^{circ}C$. TPDex showed broad dextranase activity regardless of dextran types, including dextran T2000, 742CB dextran, and alternan. TPDex showed the highest thermostability among the characterized dextranases, and may be a suitable enzyme for use in sugar manufacture without decreased temperature.