AimsThe aim of this study was to analyse the mechanism of action of p-coumaric acid against isolate B0510 of Botrytis cinerea. For this purpose, the effect of this compound on cell membrane, cell wall and oxidative phosphorylation was determined. Induction of oxidative stress triggered by this compound was also studied. Methods and Resultsp-coumaric acid showed antifungal effect on the mycelial growth. Additionally, the compound was able to retard the germination of Botrytis cinerea conidia. The mechanism of action of this compound was analysed using fluorescent probes. p-Coumaric acid did not affect the integrity of cell wall and plasmatic membrane and neither produced oxidative stress. Finally, it was shown that the compound produced an increase in oxygen consumption. Conclusionsp-coumaric acid performs as a mitochondrial uncoupler in B.cinerea. Its role as an uncoupler of oxidative phosphorylation could be explained to its acidic, nonpolar and planar characteristics. These structural and chemical characteristics would favour ability of p-coumaric acid to pass through cellular membranes. Significance and Impact of the StudyPlant secondary metabolites can be used as an alternative way to control phytopathogenic fungi. The knowledge of the action mechanism of these compounds can contribute to design modified molecules with higher antifungal activity.