An efficient ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry method was developed for separation and profiling of phytochemical constituents of Chinese wild mandarin, Mangshanju (Citrus reticulata Blanco). All constituents were well separated within 16 min. Based on retention times, accurate mass, MSE fragments and/or reference standards as well as databases, a total of 81 compounds were unambiguously identified or tentatively assigned including flavonoid glycosides, acylated flavonoid glycosides, flavones, polymethoxylated flavonoids and limonoids as well as four other compounds. Among them, 22 polymethoxylated flavones and 10 polymethoxylated flavanones/chalcones were identified in Mangshanju, more types than other citrus reported before. A basic procedure for identifying flavonoid-O-glycosides and the aglycones including polymethoxylated flavonoids was proposed. In addition, this method was successfully used to analyze another four mandarin germplasms, Cenxi suan ju, Xipi gousi gan, Nanfeng miju and Or, showing that Mangshanju contained two characteristic compounds distinct from the other four citrus species. This study systematically profiled phytochemical constituents of Mangshanju, which was helpful for further utilization of Mangshanju owing to its abundant bioactive compounds. This article is protected by copyright. All rights reserved.