Using the concept of the flow stress surface and fracture stress surface, I proposed a fundamental theory of brittle fracture of mild steel in the article entitled “Brittle Fracture of Mild Steel (The 1st Report).” In order to estimate the values of various parameters governing the flow stress surface and fracture stress surface, I have performed the tensile test of thin walled tube under internal pressure. Fairly good concurrence with experimental results have been attained by using approximately the same values of various parameters as those used in the above-mentioned article.