Activity-guided chromatographic purification of the methanol extract of Ageratum conyzoides, using pine wood nematodes Bursaphelenchus xylophilus successfully led to the isolation and characterization of the nematicidal compound with minimum effective dose (MED) of 75 μg/ cotton ball (μg/bl.). Based on the chemical and spectral properties, the compound was determined to be coumarin (1). The activity of coumarin derivatives (2-5) was also investigated.