Chisosiamols A-K (<b>1</b>-<b>11</b>), 11 new d-<i>chiro</i>-inositol derivatives, along with a known analogue (<b>12</b>) were isolated from the fruits of <i>Chisocheton siamensis</i>. Their planar structures and relative configurations were elucidated by the comprehensive application of spectroscopic methods, especially from the characteristic coupling constants, and <sup>1</sup>H-<sup>1</sup>H COSY spectra. The absolute configurations of the d-<i>chiro</i>-inositol core were determined using the ECD exciton chirality and X-ray diffraction crystallographic analytical methods. This is the first crystallographic data reported for the d-<i>chiro</i>-inositol derivatives. A structural elucidation strategy mainly combining <sup>1</sup>H-<sup>1</sup>H COSY correlations and ECD exciton chirality for determining the structure of d-<i>chiro</i>-inositol derivatives was developed, which also led to the revisions of previously reported structures. Bioactivity evaluation indicated that chisosiamols A, B, and J can reverse multidrug resistance in MCF-7/DOX cells in the IC<sub>50</sub> range of 3.4-6.5 μM (RF: 3.6-7.0).