The crystallographic structure and magnetic properties of bismuth substituted terbium-iron garnets have been studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Mössbauer spectroscopy. The crystal structures were found to be a cubic garnet structure with space group Ia3d. The lattice constants increase linearly with increasing bismuth concentration. The field-cooled magnetization curves measured at various external fields. The compensation temperature(Tcomp) were determined at 260, 170, and 120 K, for x = 0.0, 0.5, and 1.0, respectively. Bisubstituted samples have the negative value with large coercivity below Tcomp. In order to study the change of the detailed local structure on bismuth substituted samples, Mössbauer spectra were measured at various temperatures from 4.2 K to Néel temperature. Above Tcomp, the spectra for the samples consist of two sextets, and the isomer shifts at room temperature of (16a) and (24d) sites are 0.26 and 0.04 mm/s. Below Tcomp, the spectra for the samples consist of three sublattice structures (16a), (16a'), and (24d). In octahedral (16a') site, electric quadrupole splitting decreases up to -0.2 mm/s with decreasing temperature from TN to 4.2 K. Therefore, we insist that the negative magnetization is related to the local anisotropy of 16a' site by the strong covalent interaction between bismuth and iron. [ABSTRACT FROM AUTHOR]