Aim:The study was aimed at purifying the active principle from Alpinia officinarum rhizomes responsible for inhibition of swarming motility of Pseudomonas aeruginosa and analysing the mechanism of action. Methods and Results: The active compound from methanol extract of A. officinarum was purified by silica gel column chromatography followed by elution from Amberlite resin. The compound 1-(3,5-dihydroxyphenyl)-2-(methylamino)ethan-1-one, inhibited swarming motility at 12Á5 µg ml À1 . This inhibition was independent of rhamnolipid production. Real-time PCR analysis showed significant down-regulation of virulence-associated genes including T3SS exoS, exoT and flagella master regulator fleQ. Conclusions: The compound from A. officinarum inhibited swarming motility and significantly down-regulated the expression of type III secretory system effector genes exoS and exoT and flagellar master regulator fleQ genes. Significance and Impact of the Study: The study identifies a potent swarming inhibitory compound from the common medicinal plant A. officinarum and reinstates the potential of plant-derived compounds in tackling virulence properties of pathogenic bacteria. et al. 2007) and type III secretory system (T3SS) (Overhage et al. 2008) among others. In addition, swarming cells are also reported to show increased tolerance to antibiotics (Overhage et al. 2008; Lai et al. 2009). Swarming motility was found to be positively associated with clinical features of ocular keratitis (Oka et al. 2015). Although many genes have been identified that regulate swarming motility, it is a complex behaviour involving a network of several genes and pathways including quorum