Abstract: Objective To establish an HPLC-ELSD method for the determination of Lonicerae Japonicae Flos in examination of Yinqiao Jiedu granules, to investigate the phenomenon of illegal feeding. Methods Ecosil C₁₈(250 mm×4.6 mm, 5 μm) column was adopted; mobile phase was methanol-0.1% formic acid solution (63:37); ELSD detector was used. Results Maranthoidin B was used as a marker. Among 11 batches from different provinces, no batch was detected with maranthoidin B. Among 189 batches of Yinqiao Jiedu granules, maranthoidin B was detected in 116 batches, and 94 batches were above the limit. There were cases of illegal feeding. Conclusion the established method is simple and sensitive; it provides a scientific basis for better quality control of Yinqiao Jiedu granules and standardize the production behavior.