Background: JRF103, a novel pan-HER inhibitor, has shown potent activity against HER1, HER2, HER4 and EGFR in vitro. To support its first in-patient trial, a sensitive and rapid method was developed and validated using ultra-performance LC–MS/MS. Materials & methods: JRF103 was extracted from plasma using protein precipitation. Extracts were subjected to ultra-performance LC–MS/MS with electrospray ionization. Results: Separation of analyte was achieved using a 1.7-μm C18 column (2.1 × 50-mm internal diameter) with a gradient elution. The developed method was fully validated following the international guides. Conclusion: The developed method was sensitive, specific and suitable for measuring JRF103 concentration in patients with advanced solid tumors in the first in-patient study of JRF103.