The phytochemical investigation of the roots of <i>Croton crassifolius</i> led to the isolation of 16 new halimane furanoditerpenoids, crohalifuranes A-P (<b>1</b>-<b>16</b>), along with 15 known analogues, <b>17</b>-<b>31</b>. The new structures including their absolute configurations were elucidated by NMR and MS data analysis, comparison of experimental and calculated electronic circular dichroism data, single-crystal X-ray diffraction data, and chemical methods. Crohalifuranes A (<b>1</b>) and B (<b>2</b>) are <i>tetranor</i>- and 19-<i>nor</i>-halimane diterpenoids featuring a rare decahydroacenaphthene core, respectively, which might be derived from the accompanying crassifoliusin A by loss of the furan ring or the C-19 substituent. Crohalifurane C (<b>3</b>) represents the first example of a 20-<i>nor</i>-halimane diterpenoid, and crohalifurane D (<b>4</b>) is characterized by an unusual 6,20-δ-lactone moiety. All compounds were examined for their inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide in RAW264.7 cells, and <b>2</b> and <b>23</b> exhibited moderate inhibition on NO production with IC<sub>50</sub> values of 17.2 ± 1.3 and 23.7 ± 1.4 μM, respectively.