Twelve new compounds including four isoflavonolignans (1a/1b and 2a/2b), two neolignans (3a/3b), and six isoflavonoids (5–10), together with seven known compounds (4 and 11–16) were isolated from the stems of Pisonia umbellifera. The structures were elucidated on the basis of comprehensive spectroscopic analyses and ECD calculation methods. Compounds 1–3 were present as enantiomers that were successfully separated by chiral HPLC. Compounds 1a/1b and 2a/2b are the first examples of isoflavonolignans with a pyranoid ring linking up the isoflavonoid and the monolignol from nature. A putative biosynthetic pathway for the isoflavonolignans was deduced. The anti-inflammatory and cytotoxic activities for all compounds were evaluated.