[en] Many high-Tc superconducting bulk materials are inhomogeneous, containing several different phases. Such inhomogeneity is considered to lead much difficulty when applying high-Tc superconductors to electric apparatuses. Therefore, it is necessary to estimate superconducting volume fraction of each phase. In 1990 Ando and Akita (CRIEPI) proposed a convenient method to estimate superconducting volume fractions. In this paper, we advanced the Ando and Akita's method, reflecting recently developed research on magnetization. This advanced method enables more precise estimate of volume fractions. Then we performed magnetization measurements on sintered Bibased polycrystalline samples and estimated the superconducting volume fractions, which showed a reasonable tendency. We also made rough estimates from X-ray diffraction patterns of these samples. We compared these two estimates to find good correspondency. (author)