Background: SYHA1807 is a novel lysine specific demethylase 1 inhibitor being developed for the treatment of small-cell lung cancer. Aim: This study aimed to establish a ultra-performance liquid chromatography-mass spectrometry (UPLC–MS)/MS method for measuring SYHA1807 in human plasma, supporting its application in a first-in-human study. Methods: SYHA1807 was separated on an ACQUITY UPLC BEH ® C18 Column (2.1 × 50 mm, 1.7 μm) after protein precipitation of plasma samples. Mass spectrometry analysis was performed with a Xevo TQS triple quadrupole mass spectrometer utilizing a positive electronic spray ionization source. The established method was fully validated according to bioanalytical guidelines. Results & conclusion: A rapid, specific and robust UPLC–MS/MS method was first established for quantifying SYHA1807 and successfully applied in a first-in-human study.