Treatment of glycocitrine-II (1), one of the acridone alkaloids having an ortho-prehylphenol moiety isolated from Citrus plants, with m-chloroperbenzoic acid (m-CPBA) in dichloromethane gave a novel oxidation product 2, along with the known cyclization products 3 and 4. The structure of 2 was elucidated by spectrometric and X-ray crystal-lographic analyses.