Abstract: AIM　To study the structures of the epimerides of cycloclausenamide. METHODS　The structures of compound I, extracted from Clausena lansium (Lour.) Skeels, and synthesized compound III were determined by single crystal X-ray diffraction analysis. The stereo-structures of compound II and IV were also built up through Tripos force field based on crystal structures of compound I and III. RESULTS　The molecular formula and molecular weight were found to be C₁₈H₁₇O₂N and 279.34 respectively. Compound I crystallized in monoclinic system, space group P2₁ with a=0.5928(1), b=1.5014(1), c=1.6190(1) nm, V=1.4410(3) nm3, Z=4, D_x=1.288 g*cm^-3, R_f=0.075, R_w=0.073(w=1/σ²｜F｜), S=3.983; compound III crystallized in triclinic system, space group P1 with a=0.5667(1), b=1.2934(1), c=2.1119(1) nm, α=102.17(1), β=90.25(1), γ=102.65(2)°, V=1.4770(5) nm3, Z=4, D_x=1.224 g*cm^-3, R_f=0.047, R_w=0.051(w=1/σ²｜F｜), S=0.467. CONCLUSION　These results showed that compound I and III both are cycloclausenamide except that the directions of the phenyl group on C6 are different. Cycloclausenamide can form 4 pairs of epimerides but the directions of the phenyl group does not affect their energy in free state.