Bioassay directed-fractionation led to isolation of 12 compounds from the roots of Bursera tonkinensis Guillaum (Burseraceae), including burselignan, bursephenylpropane, and burseneolignan. Of the 12 compounds, only 4'-demethyldesoxypodophyllotoxin exhibited significant cytotoxic activities against KB, Col2 and LNCaP cell lilies. (c) 2005 Elsevier Ltd. All rights reserved.