Munrolins A-Q (<b>1</b>-<b>17</b>), 17 new ring C-<i>seco</i> limonoids with diverse oxidative patterns of C-12, together with nine known analogues (<b>18</b>-<b>26</b>), were isolated from the CH<sub>2</sub>Cl<sub>2</sub> extract of <i>Munronia unifoliolata</i>. The planar structures were elucidated by a combination of 1D and 2D NMR and HR-MS analyses, while the absolute configurations were confirmed by ECD calculations and single-crystal X-ray diffraction. Munrolins A (<b>1</b>) and B (<b>2</b>) were first identified as ring C-<i>seco</i> limonoids with a 12,13-ether bridge moiety. Munrolins C-J (<b>3</b>-<b>10</b>) have a rare reduced primary alcohol fragment, while munrolin Q (<b>17</b>) has an unusual ketal fragment formed by dehydration of C-12/14. These limonoids with diverse alcohol and aldehyde type C11/12 branches may be generated through different degrees of reduction after the Baeyer-Villiger oxidation at the C ring, as key intermediates to supplement the biogenetic pathway of ring C-<i>seco</i> limonoids. Compounds <b>11</b>, <b>19</b>, and <b>26</b> could reverse the multidrug resistance of MCF-7/doxorubicin cells with reversal fold values of 5.2, 4.5, and 18.3, respectively.