The powerful anti-malarial drug, Artemisinin (Qinghaosu), and the model molecule 1,2,4-trioxane in both chair and boat/twisted form have been studied by the quantum chemistry calculation method at the ab initio SCF HF and the DFT level with 6-31G* basis sets. On comparing the optimized geometry of 1,2,4-trioxane with Artemisinin, it has been found that the geometric parameters of 1,2,4-trioxane in boat/twist form is remarkablly close to that of the ring system in Artemisinin. The harmonic normal mode analysis at the B3LYP/6-31G* level shows clearly that the O–O stretching mode is actually combined with the O–C vibrational mode, having the character of O–O–C entity, as suggested by Jefford's group. The O–O vibration bands at 722, 831 and 881 cm −1 suggested by experimental studies have been assigned as 1,2,4-trioxane ring breathing coupled with -C–C–C- linkage (722 cm −1), twisting (831 cm −1), and coupled C–O and O–O stretching modes of O–O–C entity (881 cm −1), respectively.