Because of increasing levels of obesity and the development of social network platforms, the online sale of slimming beverages has become very common. However, such beverages are often reported to contain hazardous drugs, such as phenolphthalein. In the present study, we established a rapid and sensitive immunochromatography gold-labeled monoclonal antibody (mAb) (IGM) method and a fluorescence-labeled mAb (IFM) method for determining phenolphthalein in ten types of slimming tea. The monoclonal antibodies and coating antigens were produced in our laboratory. Under optimal conditions, the cut-off limits were 250 ng mL-1 (IFM strip) and 500 ng mL-1 (IGM strip) in both 0.01 M phosphate-buffered saline (PBS) and samples of slimming tea. The mean recoveries were 96.2 to 104.7% for the IGM strip and 90.7 to 104.7% for the IFM strip. The data showed that the IFM strip was more sensitive than the IGM strip and that results could be generated within 10 min. Consequently, this novel technique represents a rapid and convenient method with which to detect phenolphthalein.