BACKGROUND The whole herb of Lagochilus ilicifolius has been used as a folk medicine for treating hemostatic, inflammation and ulcer in China. There were only limited reports on its chemical constituents, and no reports on its pharmacology study. OBJECTIVE To isolate compounds from the whole herb of L. ilicifolius and evaluate their cytotoxic activity. METHODS The column chromatographic techniques were used for separating the constituents of the n-butanol-soluble fraction of the 95% ethanol extract from the whole plant of L. ilicifolius. The structures of one new lignan and two known lignans were elucidated on the basis of spectroscopic analyses and comparison with literature data. The cytotoxic activities of these three lignans were evaluated using the MTT-assay against PC12 cell line derived from rat adrenal pheochromocytoma. RESULTS The new lignan was identified as erythro-1-[(4-O-β-D-glucopyranosyl-3-methoxyl)-phenyl]-2-[(5'-methoxyl)-pinoresinol]-propane-1,3-diol (1), and two known lignans were identified as tortoside C (2) and sisymbrifolin (3). The new lignan exhibited significant cytotoxic activity against PC12 cell line with IC50 value of 1.22 ± 0.03 μmol/L. CONCLUSIONS A new lignan, erythro-1-[(4-O-β-D-glucopyranosyl-3-methoxyl)-phenyl]-2-[(5'-methoxyl)-pinoresinol]-propane-1,3-diol and two known lignans were isolated from the whole herbs of L. ilicifolius. The two known lignans were reported for the first time in the genus Lagochilus. Three lignans were evaluated for in vitro cytotoxic activity. The new lignan showed relatively strong cytotoxicity against PC12 cell line, while sisymbrifolin and tortoside C exibited no cytotoxicity.