Chemical investigation of the roots of Dictamnus radicis Cortex led to the isolation of a new limonoid isodictamdiol (1) and a known dictamdiol (2), the first 5S/9S-type degraded limonoids, together with other six known limonoids (3-8). The chemical structures were identified on the basis of modern spectroscopic methods, including IR, MS, NMR ((1)H-NMR, (13)C-NMR, (1)H-(1)H COSY, HMQC, HMBC, NOESY). Additionally, the absolute configurations of limonoid isodictamdiol (1) and dictamdiol (2) were separately elucidated by single crystal X-ray diffraction, as well as their circular dichroism spectra. Furthermore, all compounds were evaluated for antibacterial activity against three bacterial cultures.