It has already been reported by the authors that the seeds of Kintoki-carrot showed delayed germi-nation. In 1959 the authors testing the ether and ethanol extracts of every part of carrot seeds, predicted the presence of germination inhibitors in all parts of them. In further studies, the authors could success-fully isolate an inhibitor in a crystalline form the activity of which is sufficient to elucidate the cause of low germination rate of carrot seeds. The results ofthe experiments and the properties of this substance are as follows:. 1. Ground powder of dry seeds of Kintoki-carrot was extracted successively with ether, ethanol and hot water. The inhibitory activity was found in all fractions, andthe ether soluble fraction was the most active among them. 2. Ether solution of the ether, extract was shaken with dilute H2SO4, and then with N NaOH. The neutral fraction of the ether solution was placed at 5°C for 3 days, and a large amount of a white crystalline substance was formed. After the crystals were removed by filtration, the solvent was eva-porated from the filtrate to obtain an oil. The oil was placed on a silica-column and run through with n-hexane, benzol-hexane (15:85 v/v), ether-hexane (5:95 v/v) and ether-hexane (90:10 v/v) successively. The last eluted substance showed an intense inhibitory action. This inhibitory fraction was freed from the solvent and dissolved with the mixture solutionof ether-petroleum ether (20:80 v/v), and purified by passing through an alumina-column (active: inactive -4:5 w/w) and was freed from the solvent by evaporation to obtain an oil. This oil was dissolved in acetone-methanol(80:20v/v) and kept at 0°C for 2 days and then filtrated to remove a crystal formed. The filtrate wassteam-distillated under a vacuum. The distillate was dissolved with etherand the ether solution was washed with water. After evaporation of ether, it wasdissolved with petroleum ether and passed through an alumina-column (4:5 w/w). The inhibitor was eluted from the column with ether-petroleum ether mixture (5:95 v/v). The purely isolated inhibitor was obtained as a colorless oil after evaporation of the solvent. This oil was crystallized into fine colorless needles, m. p. 2_??_3°C, by standing at -10°C for 2 days. 3. The crystals of thisgermination inhibitor are easily soluble in petroleum ether, n-hexane, benzol, ether, aceton, ethanol, chloroform and carbon disul-fide, and insoluble in cold water. It has a bitter taste and a specific fragrance. It is positive in the alkali xanthate reaction, and gives a red coloration with concentrated H2SO4 and produces a brownish color with 0.2% potassium permanganate. It is negative in the diazotized benzidine reaction, and does not contain N and S in its component. The infrared absorption spectra show the presence of aromatic rings, alcoholic hydroxyl radical, and unsaturated double bond in it. The one-dimensional paperpartition chromatogram of this substance was deve-loped by ascending technique with thelower layer of methanol-petroleum ether-water (4:5:1 v/v) as solvent, and showed a spot having Rf 0.85. Ultra-violet absorption spectrum gives λmax. 258mμ. The molecular formula is C18H30O3. 4. This substance inhibited the germination of carrot seeds as well as lettuce seeds at the level 1:4, 000, and the Chinese-cabbage seeds at the level 1:500 dilution. 5. Because it seems to be an unknown substance, the authors wish to give the name “Carrotol” to this substance.