A high-performance liquid chromatography/mass spectrometry (HPLC-MS) method for the quality control of Shuang-Huang-Lian oral liquid, an antimicrobial and antipyretic herbal preparation, has been developed. Pure compounds are subjected to tandem mass spectrometry (MS(n)) analysis to clarify their fragmentation rules. Then, the sample of Shuang-Huang-Lian was analyzed by on-line LC-MS(n). A total of 27 compounds, including seven phenylethanoid glycosides, three lignans, seven quinic acids, six saponins and four flavonoids, in the extract of Shuang-Huang-Lian oral liquid have been identified or tentatively characterized. It is expected to develop a comprehensive quality control method of this commonly used herbal preparation.