3-points bending tests were performed to examine the bending strengths of three kinds of pipes consisting of porous alumna. Also, the effective volumes of those pipes were calculated in uni-axial (longitudinal) stress and multiaxial stresses, respectively. Analysis program "G-FICES was used to calculate the effective volume of the pipes in multi-axial stresses. The bending strengths of the pipes were decreased with increasing the effective volumes. Also, the calculated effective volumes in multi-axial stresses increased than that in uni-axial stress. It was found that the bending strengths of the porous alumna pipes of inner/outer diameters = 14mm/22mm, 22mm/27mm could predict from the 4-points bending strength of small specimen by using Weibull's theory when it used the effective volume in multi-axial stresses.