An unusual nor-monoterpene with only nine carbons, nor-paeonilactone (1), two new monoterpenes, paeonisuffrone C (2), paeonilactone D (9), and a new monoterpene glucoside, paeonin D (3), along with ten known compounds were isolated from the dried roots of Paeonia lactiflora. Their structures were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR, and computational data. Compounds 4–14 were evaluated for their anti-proliferative activities against BT 483 human breast cancer cells and OVCA 429 human ovarian cancer cells by MTT assay.