Two new alkaloids named polygonatine A ( 1) and polygonatine B ( 2) have been isolated from the rhizome of Polygonatum sibiricum Redoute (Liliaceae). By spectral data (IR, UV, MS, 1D and 2D NMR) and chemical evidence, their structures were elucidated as 3-hydroxymethyl-5,6,7,8-tetrahydroindolizin-8-one ( 1) and 3-ethoxymethyl-5,6,7,8-tetrahydroindolizin-8-one ( 2).