Abstract: [Objective] To investigate the relationship between quorum sensing (QS) and type III secretion system (T3SS) in Pseudomonas aeruginosa. [Methods] We constructed several gene knockout mutants of QS systems. The promoters of the T3SS genes, exoS , exoY, exoT and exsD-pscA-L were cloned and fused upstream of the luminescence reporter gene cluster, luxCDABE. The reporter constructs were integrated on the chromosome in the wild type strain PAO1 and the QS mutants respectively, and the expression of the T3SS genes in these strains was compared. [Results] The expression of exoS and exoT in pqsR mutant was increased significantly. The Rhl system repressed the activities of the four T3SS genes and the Las system had no effect. [Conclusion] The results indicate that the Rhl and Pseudomonas Quinolone Signal (PQS) systems play an important role in regulating T3SS gene expression in Pseudomonas aeruginosa.