Croton crassifolius Geisel belongs to the genus croton of the family euphorbiaceae. By means of solvent extraction and repeated chromatorgraphy on silica gel, Sephadex LH-20 and HPLC, the ethanol extract of the roots of Croton crassifolius Geisel was chemically investigated, which led to the isolation of nine diterpenoids. By using spectroscopic analysis, their structures were identified as follows： Crassifolin P（1）, Crassifolin J（2）, 1,5,6-trimethyl-5-（2-（5-oxo-2,5-dihydrofuran-3-yl）ethyl）-1,2,3,4,5,6,7,8-octahydronaphthalene-1-carboxylate（3）, Penduliflaworosin（4）, isoteucvin（5）, Crassifolin G（6）, teucvin（7）, Chettaphanin I（8）, mallotucin D（9）. Among of them compound 1 was a new compound.
