A new chromone polymorchromone B was isolated and characterized from the roots of Angelica polymorpha Maxim, a commonly used traditional Chinese medicine. On the basis of spectroscopic analysis, including IR, HR-ESI-MS, 1D and 2D NMR spectral data, and hydrolysis followed by chromatographic analysis, the structure of the new chromone was elucidated as 5-hydroxy-2-[(angeloyloxy)methyl]-2'-(dimethyl)-3'-(2S,3S-epoxy-2-methylbutanoate)-dihydropyran [3',2':6,7]chromone. Moreover, it was found that polymorchromone B showed remarkable cytotoxic activity against A-549 cell lines.