Two new hydroxychavicol analogs nudibaccatumin A (1) and B (2), together with twenty known compounds were isolated from the methanol extract of Piper nudibaccatum. Their structures were elucidated by extensive spectroscopic analyses (1D and 2D NMR, HRESIMS, UV, IR and polarimetry). Hydroxychavicol is a known inhibitor of xanthine oxidase (XO). In the present study, hydroxychavicol and 5 natural analogs (1-5) were evaluated for their XO inhibitory activity. Neotaiwanensol B (3) (IC50 = 0.28 mu M) showed a greater inhibitory effect than hydroxychavicol and allopurinol (the positive control). Two new compounds 1 and 2 showed a moderate inhibition activity with an IC50 value of 62.94 mu M and 70.67 mu M, respectively. (C) 2015 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.