Thermophilic bacterium Bacillus stearothermophilus TLS33, isolated from a hot spring in Chiang Mai, Thailand, usually produces many enzymes that are very useful for industrial applications. However, the functional properties and mechanisms of this bacterium under stress conditions are rarely reported and still need more understanding on how the bacterium can survive in stress environments. In this study, we examined the oxidative stress induced proteins of this bacterium by proteomic approach combining two-dimensional electrophoresis and mass spectrometry. When the bacterium encountered oxidative stress, peroxiredoxin, as an antioxidant enzyme, is one of the interesting stressed proteins which appeared to be systematically increased with different pI. There are four isoforms of peroxiredoxin, denoted as Prx I, Prx II, Prx III and Prx IV, which are observed at the same molecular weight of 27 kDa but differ in pI values of 5.0, 4.87, 4.81 and 4.79, respectively. The H2O2 concentration directly increased Prx II, Prx III and Prx IV intensities, but decreased Prx I intensity. These shifting of peroxiredoxin isoforms may occur by a post-translational modification. Otherwise, the longer time of oxidative stress had not affected the expression level of peroxiredoxin isoforms. Therefore, this finding of peroxiredoxin intends to know the bacterial adaptation under oxidative stress. Otherwise, this protein plays an important role in many physiological processes and able to use in the industrial applications.