In this paper, we report the experimental results of the principal stresses separation using a combination stress analysis of photoelasticity and thermoelasticity. Experimental investigation was carried out on specimens made of epoxy resin with a center hole under constant tensile loads. In case of photoelasticity test, only the difference of the stress is obtained, and in case of thermoelastic stress analysis, only the sum of the stress is measured. However, it is difficult to separate principal stress by only either of them. Then, Mohr's stresses circle was employed as the most easy and convenient method to separate of principal stresses. Moreover, by using different shape of center hole at the specimens, the change of the stress concentration factor at the vicinity of center hole of the test specimen by data of photoelasticity and thermoelastic stress analysis was obtained. The effectiveness of the principal stresses separation from the photoelastic and thermoelastic stresses measured values was verified. We also confirmed the capacity of application of the thermoelastic stress analysis to evaluate stress concentration factor.