By using a new bioassay-guided method, 2-hydroxy-4-methoxybenzaldehyde isolated from the root bark of Periploca sepium, a traditional Chinese medicine, showed repellent activity against the olive weevil (Dyscerus perforatus) at 62.5, 125, 250 and 500 mu g/disc, respectively. In addition, it also exhibited antinematodal activity against Bursaphelenchus xylophilus at a minimum effective dose of 200 mu g/ball. The three related compounds obtained were also evaluated for the above-mentioned bioactivities.