The powdered flowering branches of A. herba alba As so. was investigated. Santonin, stigmasterol and β–sitosterol, were isolated from the light petroleum extract. A crystalline substance, m. p. 277–278° C was isolated from the ethereal extract of the defatted powder and was found to be saturated, non–reducing triterpenoid; its acetyl derivative m. p. 193–195° C. The presence of santonin in A. herba alba is reported for the first time in this plant. A new method for the estimation of santonin was established. The percentage of santonin was found to be 0.99 % w/w.