Heating quinghaosu [antimalarial drug] in refluxing xylene for 22 h afforded decomposition products 2 and 4 in 15% yield each. Structures of 2 and 4 were assigned based on their 1H-NMR and 13C-NMR data and the former confirmed by a single crystal X-ray analysis. Structure 4, supported by spectral data and a successful O-acetylation of the OH group remains tentative. Structures 2 and 4 contain a newly formed tetrahydrofuran ring, originating by breakage of the original peroxide group.